DBLINK_B...QL_UPDATE(3)

okay bestie, welcome to the DBLINK_B...QL_UPDATE(3) page from the PostgreSQL 13.23 Documentation — this is the one about dblink_build_sql_update, and it's lowkey iconic for selective replication 💅✨

🎀 NAME 🎀

dblink_build_sql_update — builds an UPDATE statement using a local tuple, replacing the primary key field values with alternative supplied values.

🦋 SYNOPSIS 🦋

dblink_build_sql_update(text relname,
                        int2vector primary_key_attnums,
                        integer num_primary_key_atts,
                        text[] src_pk_att_vals_array,
                        text[] tgt_pk_att_vals_array) returns text

🌸 DESCRIPTION 🌸

Think of dblink_build_sql_update as your little selective-replication bestie: it helps copy a local table over to a remote database, but on purpose, not all willy-nilly. It picks a row from the local table using the primary key, then builds a SQL UPDATE command that duplicates that row, except the primary key values are swapped out for whatever you put in the last argument. (Want an exact copy of the row? Just pass the same values for the last two arguments, periodt.) The UPDATE command always assigns all fields of the row — and the main difference between this and dblink_build_sql_insert is that this one assumes the target row already exists in the remote table.

🧚 ARGUMENTS 🧚

• relname — name of a local relation, for example foo or myschema.mytab. Include double quotes if the name is mixed-case or contains special characters, for example "FooBar"; without quotes, the string will be folded to lower case.
• primary_key_attnums — attribute numbers (1-based) of the primary key fields, for example 1 2.
• num_primary_key_atts — the number of primary key fields.
• src_pk_att_vals_array — values of the primary key fields to be used to look up the local tuple. Each field is represented in text form. An error is thrown if there is no local row with these primary key values.
• tgt_pk_att_vals_array — values of the primary key fields to be placed in the resulting UPDATE command. Each field is represented in text form.

👑 RETURN VALUE 👑

Returns the requested SQL statement as text.

💀 NOTES 💀

As of PostgreSQL 9.0, the attribute numbers in primary_key_attnums are interpreted as logical column numbers, corresponding to the column's position in SELECT * FROM relname. Previous versions interpreted the numbers as physical column positions. There is a difference if any column(s) to the left of the indicated column have been dropped during the lifetime of the table.

🌈 EXAMPLES 🌈

Here's the vibe in action:

           SELECT dblink_build_sql_update('foo', '1 2', 2, '{"1", "a"}', '{"1", "b"}');
                              dblink_build_sql_update
           -------------------------------------------------------------
            UPDATE foo SET f1='1',f2='b',f3='1' WHERE f1='1' AND f2='b'
           (1 row)

mwah 💋 — this page is from PostgreSQL 13.23, dated 2025. now go build those UPDATE statements, bestie 🫶✨