ALTER_TABLE(7pg17)

📦 version 17.11, in opensuse-leap 16.0

💖 ALTER_TABLE — ALTER TABLE(7) 💖

PostgreSQL 17.11 Documentation ✨

💅 NAME 💅

ALTER_TABLE — change the definition of a table. That’s the whole vibe: you’re reshaping an existing table’s definition, not building a new one from scratch. 🫶

✨ SYNOPSIS ✨

okay so here’s the full synopsis, bestie — every form and every nested definition, no cap. Keep it close:

ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
    action [, ... ]
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
    RENAME [ COLUMN ] column_name TO new_column_name
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
    RENAME CONSTRAINT constraint_name TO new_constraint_name
ALTER TABLE [ IF EXISTS ] name
    RENAME TO new_name
ALTER TABLE [ IF EXISTS ] name
    SET SCHEMA new_schema
ALTER TABLE ALL IN TABLESPACE name [ OWNED BY role_name [, ... ] ]
    SET TABLESPACE new_tablespace [ NOWAIT ]
ALTER TABLE [ IF EXISTS ] name
    ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }
ALTER TABLE [ IF EXISTS ] name
    DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ]

where action is one of:

    ADD [ COLUMN ] [ IF NOT EXISTS ] column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
    DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ]
    ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ]
    ALTER [ COLUMN ] column_name SET DEFAULT expression
    ALTER [ COLUMN ] column_name DROP DEFAULT
    ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
    ALTER [ COLUMN ] column_name SET EXPRESSION AS ( expression )
    ALTER [ COLUMN ] column_name DROP EXPRESSION [ IF EXISTS ]
    ALTER [ COLUMN ] column_name ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]
    ALTER [ COLUMN ] column_name { SET GENERATED { ALWAYS | BY DEFAULT } | SET sequence_option | RESTART [ [ WITH ] restart ] } [...]
    ALTER [ COLUMN ] column_name DROP IDENTITY [ IF EXISTS ]
    ALTER [ COLUMN ] column_name SET STATISTICS { integer | DEFAULT }
    ALTER [ COLUMN ] column_name SET ( attribute_option = value [, ... ] )
    ALTER [ COLUMN ] column_name RESET ( attribute_option [, ... ] )
    ALTER [ COLUMN ] column_name SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
    ALTER [ COLUMN ] column_name SET COMPRESSION compression_method
    ADD table_constraint [ NOT VALID ]
    ADD table_constraint_using_index
    ALTER CONSTRAINT constraint_name [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
    VALIDATE CONSTRAINT constraint_name
    DROP CONSTRAINT [ IF EXISTS ]  constraint_name [ RESTRICT | CASCADE ]
    DISABLE TRIGGER [ trigger_name | ALL | USER ]
    ENABLE TRIGGER [ trigger_name | ALL | USER ]
    ENABLE REPLICA TRIGGER trigger_name
    ENABLE ALWAYS TRIGGER trigger_name
    DISABLE RULE rewrite_rule_name
    ENABLE RULE rewrite_rule_name
    ENABLE REPLICA RULE rewrite_rule_name
    ENABLE ALWAYS RULE rewrite_rule_name
    DISABLE ROW LEVEL SECURITY
    ENABLE ROW LEVEL SECURITY
    FORCE ROW LEVEL SECURITY
    NO FORCE ROW LEVEL SECURITY
    CLUSTER ON index_name
    SET WITHOUT CLUSTER
    SET WITHOUT OIDS
    SET ACCESS METHOD { new_access_method | DEFAULT }
    SET TABLESPACE new_tablespace
    SET { LOGGED | UNLOGGED }
    SET ( storage_parameter [= value] [, ... ] )
    RESET ( storage_parameter [, ... ] )
    INHERIT parent_table
    NO INHERIT parent_table
    OF type_name
    NOT OF
    OWNER TO { new_owner | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
    REPLICA IDENTITY { DEFAULT | USING INDEX index_name | FULL | NOTHING }

and partition_bound_spec is:

IN ( partition_bound_expr [, ...] ) |
FROM ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] )
  TO ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )

and column_constraint is:

[ CONSTRAINT constraint_name ]
{ NOT NULL |
  NULL |
  CHECK ( expression ) [ NO INHERIT ] |
  DEFAULT default_expr |
  GENERATED ALWAYS AS ( generation_expr ) STORED |
  GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
  UNIQUE [ NULLS [ NOT ] DISTINCT ] index_parameters |
  PRIMARY KEY index_parameters |
  REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and table_constraint is:

[ CONSTRAINT constraint_name ]
{ CHECK ( expression ) [ NO INHERIT ] |
  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( column_name [, ... ] ) index_parameters |
  PRIMARY KEY ( column_name [, ... ] ) index_parameters |
  EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE ( predicate ) ] |
  FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and table_constraint_using_index is:

    [ CONSTRAINT constraint_name ]
    { UNIQUE | PRIMARY KEY } USING INDEX index_name
    [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

index_parameters in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:

[ INCLUDE ( column_name [, ... ] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ USING INDEX TABLESPACE tablespace_name ]

exclude_element in an EXCLUDE constraint is:

{ column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]

referential_action in a FOREIGN KEY/REFERENCES constraint is:

{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( column_name [, ... ] ) ] | SET DEFAULT [ ( column_name [, ... ] ) ] }

🌸 DESCRIPTION 🌸

ALTER TABLE changes the definition of an existing table. There are several subforms described below. Note that the lock level required may differ for each subform. An ACCESS EXCLUSIVE lock is acquired unless explicitly noted. When multiple subcommands are given, the lock acquired will be the strictest one required by any subcommand. 💅

Lock check, bestie: ACCESS EXCLUSIVE is the default drama unless the page says otherwise, and when you batch subcommands, you get the strictest lock any one of them needs. 🔥

💖 ADD [ COLUMN ] [ IF NOT EXISTS ] 💖

This form adds a new column to the table, using the same syntax as CREATE TABLE. If IF NOT EXISTS is specified and a column already exists with this name, no error is thrown. ✨

🦋 DROP [ COLUMN ] [ IF EXISTS ] 🦋

This form drops a column from a table. Indexes and table constraints involving the column will be automatically dropped as well. Multivariate statistics referencing the dropped column will also be removed if the removal of the column would cause the statistics to contain data for only a single column. You will need to say CASCADE if anything outside the table depends on the column, for example, foreign key references or views. If IF EXISTS is specified and the column does not exist, no error is thrown. In this case a notice is issued instead. 🫶

💅 SET DATA TYPE 💅

This form changes the type of a column of a table. Indexes and simple table constraints involving the column will be automatically converted to use the new column type by reparsing the originally supplied expression. The optional COLLATE clause specifies a collation for the new column; if omitted, the collation is the default for the new column type. The optional USING clause specifies how to compute the new column value from the old; if omitted, the default conversion is the same as an assignment cast from old data type to new. A USING clause must be provided if there is no implicit or assignment cast from old to new type. ✨

When this form is used, the column’s statistics are removed, so running ANALYZE on the table afterwards is recommended. 🔥

🎀 SET/DROP DEFAULT 🎀

These forms set or remove the default value for a column (where removal is equivalent to setting the default value to NULL). The new default value will only apply in subsequent INSERT or UPDATE commands; it does not cause rows already in the table to change. 💖

🌈 SET/DROP NOT NULL 🌈

These forms change whether a column is marked to allow null values or to reject null values.

SET NOT NULL may only be applied to a column provided none of the records in the table contain a NULL value for the column. Ordinarily this is checked during the ALTER TABLE by scanning the entire table; however, if a valid CHECK constraint exists (and is not dropped in the same command) which proves no NULL can exist, then the table scan is skipped. 👑

If this table is a partition, one cannot perform DROP NOT NULL on a column if it is marked NOT NULL in the parent table. To drop the NOT NULL constraint from all the partitions, perform DROP NOT NULL on the parent table. Even if there is no NOT NULL constraint on the parent, such a constraint can still be added to individual partitions, if desired; that is, the children can disallow nulls even if the parent allows them, but not the other way around. 🧚

🍓 SET EXPRESSION AS 🍓

This form replaces the expression of a generated column. Existing data in the column is rewritten and all the future changes will apply the new generation expression.

When this form is used, the column’s statistics are removed, so running ANALYZE on the table afterwards is recommended. 💜

🦋 DROP EXPRESSION [ IF EXISTS ] 🦋

This form turns a stored generated column into a normal base column. Existing data in the columns is retained, but future changes will no longer apply the generation expression.

If DROP EXPRESSION IF EXISTS is specified and the column is not a stored generated column, no error is thrown. In this case a notice is issued instead. ✨

💫 ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY, SET GENERATED { ALWAYS | BY DEFAULT }, DROP IDENTITY [ IF EXISTS ] 💫

These forms change whether a column is an identity column or change the generation attribute of an existing identity column. See CREATE TABLE for details. Like SET DEFAULT, these forms only affect the behavior of subsequent INSERT and UPDATE commands; they do not cause rows already in the table to change.

If DROP IDENTITY IF EXISTS is specified and the column is not an identity column, no error is thrown. In this case a notice is issued instead. 🫶

🔥 SET sequence_option / RESTART 🔥

These forms alter the sequence that underlies an existing identity column. sequence_option is an option supported by ALTER SEQUENCE such as INCREMENT BY. 🎀

🎀 SET STATISTICS 🎀

okay so this one sets the per-column statistics-gathering target for all the ANALYZE operations that come after it. you can set the target anywhere in the range 0 to 10000. set it to DEFAULT and it reverts to using the system default statistics target (default_statistics_target). (and setting it to -1 is like, an obsolete way of spelling it that gets the same outcome — so it works, but it's giving legacy, bestie.) for more info on how the PostgreSQL query planner uses statistics, go peek at Section 14.2.

SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. noted 💅

🌸 SET ( attribute_option = value [, ... ] ) / RESET ( attribute_option [, ... ] ) 🌸

this form sets or resets per-attribute options. rn the only defined per-attribute options are n_distinct and n_distinct_inherited, and they override the number-of-distinct-values estimates that get made by subsequent ANALYZE operations.

  • n_distinct affects the statistics for the table itself
  • n_distinct_inherited affects the statistics gathered for the table plus its inheritance children, and for the statistics gathered for partitioned tables

when the value you specify is a positive value, the query planner will assume the column contains exactly the specified number of distinct nonnull values. fractional values are also a thing — you specify them by using values below 0 and above or equal to -1. that tells the query planner to estimate the number of distinct values by multiplying the absolute value of the specified number by the estimated number of rows in the table. for example, a value of -1 implies that all values in the column are distinct, while a value of -0.5 implies that each value appears twice on average. this can be useful when the size of the table changes over time. for more info on how the PostgreSQL query planner uses statistics, refer to Section 14.2.

changing per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock. 🔒

🦋 SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT } 🦋

this form sets the storage mode for a column, and it controls whether the column is held inline or in a secondary TOAST table, plus whether the data should be compressed or not. let's break it down:

  • PLAIN — must be used for fixed-length values such as integer, and it's inline, uncompressed.
  • MAIN — for inline, compressible data.
  • EXTERNAL — for external, uncompressed data.
  • EXTENDED — for external, compressed data.
  • DEFAULT — writing this sets the storage mode to the default mode for the column's data type.

EXTENDED is the default for most data types that support non-PLAIN storage. using EXTERNAL will make substring operations on very large text and bytea values run faster — at the penalty of increased storage space, so, tradeoffs, iykyk.

heads up: ALTER TABLE ... SET STORAGE doesn't itself change anything in the table; it just sets the strategy to be pursued during future table updates. see Section 65.2 for more info. 🫶

🧚 SET COMPRESSION compression_method 🧚

this form sets the compression method for a column, determining how values inserted in future will be compressed (if the storage mode permits compression at all). it does not cause the table to be rewritten, so existing data may still be compressed with other compression methods. if the table is restored with pg_restore, then all values are rewritten with the configured compression method. but — plot twist — when data is inserted from another relation (for example, by INSERT ... SELECT), values from the source table are not necessarily detoasted, so any previously compressed data may retain its existing compression method rather than being recompressed with the compression method of the target column. 🙈

the supported compression methods are pglz and lz4. (lz4 is available only if --with-lz4 was used when building PostgreSQL.) in addition, compression_method can be default, which selects the default behavior of consulting the default_toast_compression setting at the time of data insertion to determine the method to use. ✨

👑 ADD table_constraint [ NOT VALID ] 👑

this form adds a new constraint to a table using the same constraint syntax as CREATE TABLE, plus the option NOT VALID, which is currently only allowed for foreign key and CHECK constraints.

normally this form will cause a scan of the table to verify that all existing rows in the table satisfy the new constraint. but if you use the NOT VALID option, this potentially-lengthy scan gets skipped. the constraint will still be enforced against subsequent inserts or updates (like, they'll fail unless there's a matching row in the referenced table, in the case of foreign keys, or they'll fail unless the new row matches the specified check condition). but the database will not assume the constraint holds for all rows in the table until it's validated by using the VALIDATE CONSTRAINT option. see Notes below for more about using the NOT VALID option.

even though most forms of ADD table_constraint require an ACCESS EXCLUSIVE lock, ADD FOREIGN KEY requires only a SHARE ROW EXCLUSIVE lock. and note that ADD FOREIGN KEY also acquires a SHARE ROW EXCLUSIVE lock on the referenced table, in addition to the lock on the table on which the constraint is declared. two locks, one vibe check. 💀

additional restrictions apply when unique or primary key constraints are added to partitioned tables — see CREATE TABLE. also, foreign key constraints on partitioned tables may not be declared NOT VALID at present. 😭

⭐ ADD table_constraint_using_index ⭐

this form adds a new PRIMARY KEY or UNIQUE constraint to a table based on an existing unique index. all the columns of the index will be included in the constraint.

the index cannot have expression columns, and it can't be a partial index. also, it must be a b-tree index with default sort ordering. these restrictions ensure the index is equivalent to one that would be built by a regular ADD PRIMARY KEY or ADD UNIQUE command. no shortcuts that break stuff, bestie. 💅

if PRIMARY KEY is specified, and the index's columns are not already marked NOT NULL, then this command will attempt to do ALTER COLUMN SET NOT NULL against each such column. that requires a full table scan to verify the column(s) contain no nulls. in all other cases, this is a fast operation. ⚡

if a constraint name is provided then the index will be renamed to match the constraint name. otherwise the constraint will be named the same as the index.

after this command is executed, the index is "owned" by the constraint, in the same way as if the index had been built by a regular ADD PRIMARY KEY or ADD UNIQUE command. in particular, dropping the constraint will make the index disappear too. gone, periodt.

this form is not currently supported on partitioned tables.

Note adding a constraint using an existing index can be helpful in situations where a new constraint needs to be added without blocking table updates for a long time. to do that, create the index using CREATE UNIQUE INDEX CONCURRENTLY, and then convert it to a constraint using this syntax. see the example below. 🫶

💜 ALTER CONSTRAINT 💜

this form alters the attributes of a constraint that was previously created. currently only foreign key constraints may be altered. that's it, that's the whole vibe.

🌈 VALIDATE CONSTRAINT 🌈

this form validates a foreign key or check constraint that was previously created as NOT VALID, by scanning the table to ensure there are no rows for which the constraint is not satisfied. nothing happens if the constraint is already marked valid. (see Notes below for an explanation of the usefulness of this command — it's lowkey the payoff of the NOT VALID trick.)

this command acquires a SHARE UPDATE EXCLUSIVE lock. 🔒

🎀 DROP CONSTRAINT [ IF EXISTS ] 🎀

this form drops the specified constraint on a table, along with any index underlying the constraint. if IF EXISTS is specified and the constraint does not exist, no error is thrown — instead a notice is issued. so chill, no dramatic failure. 🦋

🔥 DISABLE/ENABLE [ REPLICA | ALWAYS ] TRIGGER 🔥

these forms configure the firing of trigger(s) belonging to the table. a disabled trigger is still known to the system, but it is not executed when its triggering event occurs. (for a deferred trigger, the enable status is checked when the event occurs, not when the trigger function is actually executed — important detail, don't skip it.) you can disable or enable a single trigger specified by name, or all triggers on the table, or only user triggers (this option excludes internally generated constraint triggers, such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints).

disabling or enabling internally generated constraint triggers requires superuser privileges — and it should be done with caution, since of course the integrity of the constraint cannot be guaranteed if the triggers are not executed. like, that's the whole point of the constraint, bestie. 💀

the trigger firing mechanism is also affected by the configuration variable session_replication_role. simply enabled triggers (the default) will fire when the replication role is "origin" (the default) or "local". triggers configured as ENABLE REPLICA will only fire if the session is in "replica" mode, and triggers configured as ENABLE ALWAYS will fire regardless of the current replication role.

the effect of this mechanism is that in the default configuration, triggers do not fire on replicas. this is useful because if a trigger is used on the origin to propagate data between tables, then the replication system will also replicate the propagated data; so the trigger should not fire a second time on the replica, because that would lead to duplication. however, if a trigger is used for another purpose such as creating external alerts, then it might be appropriate to set it to ENABLE ALWAYS so it's also fired on replicas. slay, customization. ✨

when this command is applied to a partitioned table, the states of corresponding clone triggers in the partitions are updated too, unless ONLY is specified.

this command acquires a SHARE ROW EXCLUSIVE lock. 🔒

🍓 DISABLE/ENABLE [ REPLICA | ALWAYS ] RULE 🍓

these forms configure the firing of rewrite rules belonging to the table. a disabled rule is still known to the system, but is not applied during query rewriting. the semantics are as for disabled/enabled triggers. 🫶

this configuration is ignored for ON SELECT rules, which are always applied in order to keep views working even if the current session is in a non-default replication role. views gotta view, no cap. 💅

The rule firing mechanism also gets affected by the config variable session_replication_role, bestie — analogous to triggers, as described above. 🌀

🛡️ DISABLE/ENABLE ROW LEVEL SECURITY

These forms control how row security policies belonging to the table get applied. If enabled and no policies exist for the table, then a default-deny policy is applied. Note that policies can exist for a table even if row-level security is disabled. In this case, the policies will not be applied and the policies will be ignored. See also CREATE POLICY. 💅

💅 NO FORCE/FORCE ROW LEVEL SECURITY

These forms control how row security policies belonging to the table get applied when the user is the table owner. If enabled, row-level security policies will be applied when the user is the table owner. If disabled (the default) then row-level security will not be applied when the user is the table owner. See also CREATE POLICY. 👑

📌 CLUSTER ON

This form selects the default index for future CLUSTER operations. It does not actually re-cluster the table. Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock. 🔒

🧹 SET WITHOUT CLUSTER

This form removes the most recently used CLUSTER index specification from the table. This affects future cluster operations that don't specify an index. Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock. 🔒

💀 SET WITHOUT OIDS

Backward-compatible syntax for removing the oid system column. As oid system columns cannot be added anymore, this never has an effect. It's giving "legacy syntax moment," no cap.

🧵 SET ACCESS METHOD

This form changes the access method of the table by rewriting it using the indicated access method; specifying DEFAULT selects the access method set as the default_table_access_method configuration parameter. See Chapter 61 for more information.

When applied to a partitioned table, there is no data to rewrite, but partitions created afterwards will default to the given access method unless overridden by a USING clause. Specifying DEFAULT removes a previous value, causing future partitions to default to default_table_access_method.

🗄️ SET TABLESPACE

This form changes the table's tablespace to the specified tablespace and moves the data file(s) associated with the table to the new tablespace. Indexes on the table, if any, are not moved; but they can be moved separately with additional SET TABLESPACE commands. When applied to a partitioned table, nothing is moved, but any partitions created afterwards with CREATE TABLE PARTITION OF will use that tablespace, unless overridden by a TABLESPACE clause.

All tables in the current database in a tablespace can be moved by using the ALL IN TABLESPACE form, which will lock all tables to be moved first and then move each one. This form also supports OWNED BY, which will only move tables owned by the roles specified. If the NOWAIT option is specified then the command will fail if it is unable to acquire all of the locks required immediately. Note that system catalogs are not moved by this command; use ALTER DATABASE or explicit ALTER TABLE invocations instead if desired. The information_schema relations are not considered part of the system catalogs and will be moved. See also CREATE TABLESPACE. 🫶

🔄 SET { LOGGED | UNLOGGED }

This form changes the table from unlogged to logged or vice-versa (see UNLOGGED). It cannot be applied to a temporary table. 🙈

This also changes the persistence of any sequences linked to the table (for identity or serial columns). However, it is also possible to change the persistence of such sequences separately.

🧺 SET ( storage_parameter [= value] [, ... ] )

This form changes one or more storage parameters for the table. See Storage Parameters in the CREATE TABLE documentation for details on the available parameters. Note that the table contents will not be modified immediately by this command; depending on the parameter you might need to rewrite the table to get the desired effects. That can be done with VACUUM FULL, CLUSTER or one of the forms of ALTER TABLE that forces a table rewrite. For planner related parameters, changes will take effect from the next time the table is locked so currently executing queries will not be affected.

SHARE UPDATE EXCLUSIVE lock will be taken for fillfactor, toast and autovacuum storage parameters, as well as the planner parameter parallel_workers.

♻️ RESET ( storage_parameter [, ... ] )

This form resets one or more storage parameters to their defaults. As with SET, a table rewrite might be needed to update the table entirely.

👶 INHERIT parent_table

This form adds the target table as a new child of the specified parent table. Subsequently, queries against the parent will include records of the target table. To be added as a child, the target table must already contain all the same columns as the parent (it could have additional columns, too). The columns must have matching data types, and if they have NOT NULL constraints in the parent then they must also have NOT NULL constraints in the child.

There must also be matching child-table constraints for all CHECK constraints of the parent, except those marked non-inheritable (that is, created with ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT) in the parent, which are ignored; all child-table constraints matched must not be marked non-inheritable. Currently UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints are not considered, but this might change in the future. 👀

✂️ NO INHERIT parent_table

This form removes the target table from the list of children of the specified parent table. Queries against the parent table will no longer include records drawn from the target table.

🧬 OF type_name

This form links the table to a composite type as though CREATE TABLE OF had formed it. The table's list of column names and types must precisely match that of the composite type. The table must not inherit from any other table. These restrictions ensure that CREATE TABLE OF would permit an equivalent table definition.

🚫 NOT OF

This form dissociates a typed table from its type. Slay, detachment era. 🦋

👑 OWNER TO

This form changes the owner of the table, sequence, view, materialized view, or foreign table to the specified user.

📼 REPLICA IDENTITY

This form changes the information which is written to the write-ahead log to identify rows which are updated or deleted. In most cases, the old value of each column is only logged if it differs from the new value; however, if the old value is stored externally, it is always logged regardless of whether it changed. This option has no effect except when logical replication is in use.

  • DEFAULT — Records the old values of the columns of the primary key, if any. This is the default for non-system tables.
  • USING INDEX index_name — Records the old values of the columns covered by the named index, that must be unique, not partial, not deferrable, and include only columns marked NOT NULL. If this index is dropped, the behavior is the same as NOTHING.
  • FULL — Records the old values of all columns in the row.
  • NOTHING — Records no information about the old row. This is the default for system tables.

✏️ RENAME

The RENAME forms change the name of a table (or an index, sequence, view, materialized view, or foreign table), the name of an individual column in a table, or the name of a constraint of the table. When renaming a constraint that has an underlying index, the index is renamed as well. There is no effect on the stored data.

🗂️ SET SCHEMA

This form moves the table into another schema. Associated indexes, constraints, and sequences owned by table columns are moved as well.

🧩 ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }

This form attaches an existing table (which might itself be partitioned) as a partition of the target table. The table can be attached as a partition for specific values using FOR VALUES or as a default partition by using DEFAULT. For each index in the target table, if a valid equivalent index already exists in the partition, it will be attached to the target table's index, as if ALTER INDEX ATTACH PARTITION had been executed; otherwise, a new corresponding index will be created. Invalid indexes on the partition are skipped. Note that if the existing table is a foreign table, it is currently not allowed to attach the table as a partition of the target table if there are UNIQUE indexes on the target table. (See also CREATE FOREIGN TABLE (CREATE_FOREIGN_TABLE(7)).) For each user-defined row-level trigger that exists in the target table, a corresponding one is created in the attached table. ✨

A partition using FOR VALUES uses same syntax for partition_bound_spec as CREATE TABLE. The partition bound specification must correspond to the partitioning strategy and partition key of the target table. The table to be attached must have all the same columns as the target table and no more; moreover, the column types must also match. Also, it must have all the NOT NULL and CHECK constraints of the target table, not marked NO INHERIT. Currently FOREIGN KEY constraints are not considered. UNIQUE and PRIMARY KEY constraints from the parent table will be created in the partition, if they don't already exist.

If the new partition is a regular table, a full table scan is performed to check that existing rows in the table do not violate the partition constraint. It is possible to avoid this scan by adding a valid CHECK constraint to the table that allows only rows satisfying the desired partition constraint before running this command. The CHECK constraint will be used to determine that the table need not be scanned to validate the partition constraint. This does not work, however, if any of the partition keys is an expression and the partition does not accept NULL values. If attaching a list partition that will not accept NULL values, also add a NOT NULL constraint to the partition key column, unless it's an expression. 🫡

If the new partition is a foreign table, literally nothing gets done to verify that all the rows in the foreign table obey the partition constraint. (Peep the discussion in CREATE FOREIGN TABLE (CREATE_FOREIGN_TABLE(7)) about constraints on the foreign table, iykyk.)

When a table has a default partition, defining a new partition changes the partition constraint for the default partition. The default partition can't contain any rows that would need to be moved to the new partition, and it will be scanned to verify that none are present. This scan, like the scan of the new partition, can be avoided if an appropriate CHECK constraint is present. Also like the scan of the new partition, it is always skipped when the default partition is a foreign table.

Attaching a partition acquires a SHARE UPDATE EXCLUSIVE lock on the parent table, in addition to the ACCESS EXCLUSIVE locks on the table being attached and on the default partition (if any).

Further locks must also be held on all sub-partitions if the table being attached is itself a partitioned table. Likewise if the default partition is itself a partitioned table. The locking of the sub-partitions can be avoided by adding a CHECK constraint as described in Section 5.12.2.2.

🎀 DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ] 🎀

This form detaches the specified partition of the target table. The detached partition continues to exist as a standalone table, but no longer has any ties to the table from which it was detached. Any indexes that were attached to the target table's indexes are detached. Any triggers that were created as clones of those in the target table are removed. SHARE lock is obtained on any tables that reference this partitioned table in foreign key constraints.

If CONCURRENTLY is specified, it runs using a reduced lock level to avoid blocking other sessions that might be accessing the partitioned table. In this mode, two transactions are used internally. During the first transaction, a SHARE UPDATE EXCLUSIVE lock is taken on both parent table and partition, and the partition is marked as undergoing detach; at that point, the transaction is committed and all other transactions using the partitioned table are waited for. Once all those transactions have completed, the second transaction acquires SHARE UPDATE EXCLUSIVE on the partitioned table and ACCESS EXCLUSIVE on the partition, and the detach process completes. A CHECK constraint that duplicates the partition constraint is added to the partition. CONCURRENTLY cannot be run in a transaction block and is not allowed if the partitioned table contains a default partition.

If FINALIZE is specified, a previous DETACH CONCURRENTLY invocation that was canceled or interrupted is completed. At most one partition in a partitioned table can be pending detach at a time.

All the forms of ALTER TABLE that act on a single table, except RENAME, SET SCHEMA, ATTACH PARTITION, and DETACH PARTITION can be combined into a list of multiple alterations to be applied together. For example, it is possible to add several columns and/or alter the type of several columns in a single command. This is particularly useful with large tables, since only one pass over the table need be made.

You must own the table to use ALTER TABLE. To change the schema or tablespace of a table, you must also have CREATE privilege on the new schema or tablespace. To add the table as a new child of a parent table, you must own the parent table as well. Also, to attach a table as a new partition of the table, you must own the table being attached. To alter the owner, you must be able to SET ROLE to the new owning role, and that role must have CREATE privilege on the table's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the table. However, a superuser can alter ownership of any table anyway.) To add a column or alter a column type or use the OF clause, you must also have USAGE privilege on the data type.

✨ PARAMETERS ✨

  • IF EXISTS — Do not throw an error if the table does not exist. A notice is issued in this case. 💅
  • name — The name (optionally schema-qualified) of an existing table to alter. If ONLY is specified before the table name, only that table is altered. If ONLY is not specified, the table and all its descendant tables (if any) are altered. Optionally, * can be specified after the table name to explicitly indicate that descendant tables are included. 🫶
  • column_name — Name of a new or existing column.
  • new_column_name — New name for an existing column.
  • new_name — New name for the table.
  • data_type — Data type of the new column, or new data type for an existing column.
  • table_constraint — New table constraint for the table.
  • constraint_name — Name of a new or existing constraint.
  • CASCADE — Automatically drop objects that depend on the dropped column or constraint (for example, views referencing the column), and in turn all objects that depend on those objects (see Section 5.15). 🔥
  • RESTRICT — Refuse to drop the column or constraint if there are any dependent objects. This is the default behavior.
  • trigger_name — Name of a single trigger to disable or enable.
  • ALL — Disable or enable all triggers belonging to the table. (This requires superuser privilege if any of the triggers are internally generated constraint triggers, such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints.)
  • USER — Disable or enable all triggers belonging to the table except for internally generated constraint triggers, such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints.
  • index_name — The name of an existing index.
  • storage_parameter — The name of a table storage parameter.
  • value — The new value for a table storage parameter. This might be a number or a word depending on the parameter.
  • parent_table — A parent table to associate or de-associate with this table.
  • new_owner — The user name of the new owner of the table.
  • new_access_method — The name of the access method to which the table will be converted.
  • new_tablespace — The name of the tablespace to which the table will be moved.
  • new_schema — The name of the schema to which the table will be moved.
  • partition_name — The name of the table to attach as a new partition or to detach from this table.
  • partition_bound_spec — The partition bound specification for a new partition. Refer to CREATE TABLE (CREATE_TABLE(7)) for more details on the syntax of the same. 🦋

💅 NOTES 💅

okay bestie, this is the part where we spill the actual behind-the-scenes tea ☕✨

First tiny thing: the key word COLUMN is literally just noise — you can omit it, no cap. 🎀

So when you add a column with ADD COLUMN and you give it a non-volatile DEFAULT, the default gets evaluated at the time of the statement and the result gets stored in the table's metadata. That value is what gets used for the column for all existing rows. If you don't specify a DEFAULT, then NULL is used. And in neither case is a rewrite of the table required. slay, no heavy lifting 💅

But — and this is the plot twist 😭 — adding a column with a volatile DEFAULT, or changing the type of an existing column, will require the entire table and its indexes to be rewritten. As an exception (yes there's an exception, keep up 🦋), when you're changing the type of an existing column, if the USING clause does not change the column contents and the old type is either binary coercible to the new type or an unconstrained domain over the new type, then a table rewrite is not needed.

However 💀 indexes must always be rebuilt unless the system can verify that the new index would be logically equivalent to the existing one. Example time: if the collation for a column has been changed, an index rebuild is always required, because the new sort order might be different. But in the absence of a collation change, a column can be changed from text to varchar (or vice versa) without rebuilding the indexes, because these data types sort identically. iconic behavior honestly.

Table and/or index rebuilds may take a significant amount of time for a large table, and will temporarily require as much as double the disk space. 🫠 plan accordingly bestie.

Adding a CHECK or NOT NULL constraint requires scanning the table to verify that existing rows meet the constraint, but does not require a table rewrite. 🎀

Similarly, when attaching a new partition it may be scanned to verify that existing rows meet the partition constraint.

And here's the real reason the option to specify multiple changes in a single ALTER TABLE even exists: multiple table scans or rewrites can thereby be combined into a single pass over the table. efficiency queen 👑

Scanning a large table to verify a new foreign key or check constraint can take a long time, and other updates to the table are locked out until the ALTER TABLE ADD CONSTRAINT command is committed. The main purpose of the NOT VALID constraint option is to reduce the impact of adding a constraint on concurrent updates.

With NOT VALID, the ADD CONSTRAINT command does not scan the table and can be committed immediately. After that, a VALIDATE CONSTRAINT command can be issued to verify that existing rows satisfy the constraint. The validation step does not need to lock out concurrent updates, since it knows that other transactions will be enforcing the constraint for rows that they insert or update — only pre-existing rows need to be checked. ✨

Hence, validation acquires only a SHARE UPDATE EXCLUSIVE lock on the table being altered. (If the constraint is a foreign key then a ROW SHARE lock is also required on the table referenced by the constraint.) 🦋

Beyond improving concurrency, it can be useful to use NOT VALID and VALIDATE CONSTRAINT in cases where the table is known to contain pre-existing violations. Once the constraint is in place, no new violations can be inserted, and the existing problems can be corrected at leisure until VALIDATE CONSTRAINT finally succeeds. lowkey a whole vibe 💜

The DROP COLUMN form does not physically remove the column — it simply makes it invisible to SQL operations. 😶‍🌫️ Subsequent insert and update operations in the table will store a null value for the column. So dropping a column is quick, but it will not immediately reduce the on-disk size of your table, because the space occupied by the dropped column is not reclaimed. The space will be reclaimed over time as existing rows are updated. it's giving "out of sight, out of mind" 🙈

To force immediate reclamation of space occupied by a dropped column, you can execute one of the forms of ALTER TABLE that performs a rewrite of the whole table. This results in reconstructing each row with the dropped column replaced by a null value. 🔥

⚠️ The rewriting forms of ALTER TABLE are not MVCC-safe. After a table rewrite, the table will appear empty to concurrent transactions, if they are using a snapshot taken before the rewrite occurred. See Section 13.6 for more details. this is the serious part, bestie, don't skip it 💀

The USING option of SET DATA TYPE can actually specify any expression involving the old values of the row — meaning it can refer to other columns as well as the one being converted. This allows very general conversions to be done with the SET DATA TYPE syntax. main character energy fr 💅

But because of this flexibility, the USING expression is not applied to the column's default value (if any); the result might not be a constant expression as required for a default. This means that when there is no implicit or assignment cast from old to new type, SET DATA TYPE might fail to convert the default even though a USING clause is supplied. 😭

In such cases, the move is: drop the default with DROP DEFAULT, perform the ALTER TYPE, and then use SET DEFAULT to add a suitable new default. Similar considerations apply to indexes and constraints involving the column. 🎀

Okay, inheritance drama incoming 🌸

If a table has any descendant tables, it is not permitted to add, rename, or change the type of a column in the parent table without doing the same to the descendants. This ensures that the descendants always have columns matching the parent.

Similarly, a CHECK constraint cannot be renamed in the parent without also renaming it in all descendants, so that CHECK constraints also match between the parent and its descendants. (That restriction does not apply to index-based constraints, however. 🦋)

Also, because selecting from the parent also selects from its descendants, a constraint on the parent cannot be marked valid unless it is also marked valid for those descendants. And in all of these cases, ALTER TABLE ONLY will be rejected. nope, denied, not today 💀

A recursive DROP COLUMN operation will remove a descendant table's column only if the descendant does not inherit that column from any other parents and never had an independent definition of the column.

A nonrecursive DROP COLUMN (i.e., ALTER TABLE ONLY ... DROP COLUMN) never removes any descendant columns, but instead marks them as independently defined rather than inherited. Also, a nonrecursive DROP COLUMN command will fail for a partitioned table, because all partitions of a table must have the same columns as the partitioning root. 🙈

Now, who recurses and who doesn't — the seating chart of ALTER TABLE 👑

  • The actions for identity columns (ADD GENERATED, SET etc., DROP IDENTITY), as well as the actions CLUSTER, OWNER, and TABLESPACE never recurse to descendant tables; that is, they always act as though ONLY were specified.
  • Actions affecting trigger states recurse to partitions of partitioned tables (unless ONLY is specified), but never to traditional-inheritance descendants.
  • Adding a constraint recurses only for CHECK constraints that are not marked NO INHERIT.

Changing any part of a system catalog table is not permitted. 🚫 do not touch, hands off, periodt 💅

Refer to CREATE TABLE (CREATE_TABLE(7)) for a further description of valid parameters. Chapter 5 has further information on inheritance. 📖

✨ EXAMPLES ✨

Bestie, let’s get practical 💅. Want to add a varchar column to a table? Slap this down:

ALTER TABLE distributors ADD COLUMN address varchar(30);

That makes every existing row in the table get filled with null values for the new column. Not me explaining defaults, but here we are 🫶.

Want a new column with a non-null default? Easy:

ALTER TABLE measurements
  ADD COLUMN mtime timestamp with time zone DEFAULT now();

Existing rows get filled with the current time as the new column’s value, and then new rows receive the time of their insertion. Timestamp girlie behavior, honestly iconic ⏰✨.

Want to add a column and fill it with a value that’s different from the default you’ll use later? Do this two-step:

ALTER TABLE transactions
  ADD COLUMN status varchar(30) DEFAULT 'old',
  ALTER COLUMN status SET default 'current';

Existing rows get filled with old, but then the default for subsequent commands is current. The effects are the same as if the two sub-commands had been issued in separate ALTER TABLE commands. Same energy, same result 💖.

Dropping a column from a table? Here:

ALTER TABLE distributors DROP COLUMN address RESTRICT;

Changing the types of two existing columns in one operation? Slay, one command:

ALTER TABLE distributors
    ALTER COLUMN address TYPE varchar(80),
    ALTER COLUMN name TYPE varchar(100);

Changing an integer column containing Unix timestamps to timestamp with time zone via a USING clause? This is the moment:

ALTER TABLE foo
    ALTER COLUMN foo_timestamp SET DATA TYPE timestamp with time zone
    USING
        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';

Same thing, but when the column has a default expression that won’t automatically cast to the new data type? Drop the default, change the type with USING, then set the default again:

ALTER TABLE foo
    ALTER COLUMN foo_timestamp DROP DEFAULT,
    ALTER COLUMN foo_timestamp TYPE timestamp with time zone
    USING
        timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
    ALTER COLUMN foo_timestamp SET DEFAULT now();

Renaming an existing column? Cute and simple:

ALTER TABLE distributors RENAME COLUMN address TO city;

Renaming an existing table? Also cute:

ALTER TABLE distributors RENAME TO suppliers;

Renaming an existing constraint? Yes bestie, constraints have names too:

ALTER TABLE distributors RENAME CONSTRAINT zipchk TO zip_check;

Adding a not-null constraint to a column? Do it:

ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;

Removing a not-null constraint from a column? Also do it:

ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;

Adding a check constraint to a table and all its children? Here’s the vibe:

ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);

Adding a check constraint only to a table and not to its children? Use NO INHERIT:

ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5) NO INHERIT;
The check constraint will not be inherited by future children, either. Important detail, no cap 🔥.

Removing a check constraint from a table and all its children? Easy:

ALTER TABLE distributors DROP CONSTRAINT zipchk;

Removing a check constraint from one table only? Use ONLY:

ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;
The check constraint remains in place for any child tables. So yeah, ONLY is doing exactly what it says 💀.

Adding a foreign key constraint to a table? Big relationship energy:

ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address);

Adding a foreign key constraint to a table with the least impact on other work? Split it into NOT VALID and then validate:

ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) NOT VALID;
ALTER TABLE distributors VALIDATE CONSTRAINT distfk;

Adding a (multicolumn) unique constraint to a table? Multicolumn uniqueness, periodt:

ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);

Adding an automatically named primary key constraint to a table? Do this — and remember, a table can only ever have one primary key 👑:

ALTER TABLE distributors ADD PRIMARY KEY (dist_id);

Moving a table to a different tablespace? Relocate the girlie:

ALTER TABLE distributors SET TABLESPACE fasttablespace;

Moving a table to a different schema? Also relocate the girlie:

ALTER TABLE myschema.distributors SET SCHEMA yourschema;

Recreating a primary key constraint, without blocking updates while the index is rebuilt? This is the big-brain move:

CREATE UNIQUE INDEX CONCURRENTLY dist_id_temp_idx ON distributors (dist_id);
ALTER TABLE distributors DROP CONSTRAINT distributors_pkey,
    ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;

Attaching a partition to a range-partitioned table? Range partition realness:

ALTER TABLE measurement
    ATTACH PARTITION measurement_y2016m07 FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');

Attaching a partition to a list-partitioned table? List partition realness:

ALTER TABLE cities
    ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');

Attaching a partition to a hash-partitioned table? Hash partition realness:

ALTER TABLE orders
    ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);

Attaching a default partition to a partitioned table? Default partition realness:

ALTER TABLE cities
    ATTACH PARTITION cities_partdef DEFAULT;

Detaching a partition from a partitioned table? Let her go 🦋:

ALTER TABLE measurement
    DETACH PARTITION measurement_y2015m12;

💖 COMPATIBILITY 💖

Okay so, the SQL-standard conforming forms are: ADD (without USING INDEX), DROP [COLUMN], DROP IDENTITY, RESTART, SET DEFAULT, SET DATA TYPE (without USING), SET GENERATED, and SET sequence_option. Those are the ones that conform with the SQL standard ✨.

The other forms are PostgreSQL extensions of the SQL standard. Also, the ability to specify more than one manipulation in a single ALTER TABLE command is an extension. Very “we added extra sprinkles” of PostgreSQL, honestly 🎀.

One big caveat: ALTER TABLE DROP COLUMN can be used to drop the only column of a table, leaving a zero-column table. This is an extension of SQL, which disallows zero-column tables. So yes, PostgreSQL will let you create that chaotic zero-column situation, but SQL itself says no 💀.

🦋 SEE ALSO 🦋

Go read CREATE TABLE (CREATE_TABLE(7)) next, bestie. It’s giving required reading 📚💖.

Mwah 💋 — this page is PostgreSQL 17.11, dated 2026, and it’s the ALTER TABLE(7) girlie signing off 🫶✨.

📦 where this page comes from