SET_CONSTRAINTS(7pg13)

💖 NAME 💖

Okay bestie, welcome to the SET CONSTRAINTS(7) page from the PostgreSQL 13.23 docs — this is the manual for SET_CONSTRAINTS, and it does exactly one iconic thing: set constraint check timing for the current transaction. That’s the vibe. ✨

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🌸 SYNOPSIS 🌸

SET CONSTRAINTS { ALL | name [, ...] } { DEFERRED | IMMEDIATE }

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🦋 DESCRIPTION 🦋

So SET CONSTRAINTS sets the behavior of constraint checking within the current transaction. IMMEDIATE constraints are checked at the end of each statement. DEFERRED constraints are not checked until transaction commit. Each constraint has its own IMMEDIATE or DEFERRED mode — no shared setting, they each have their own little setting. 💅

When a constraint is created, it gets one of three characteristics: DEFERRABLE INITIALLY DEFERRED, DEFERRABLE INITIALLY IMMEDIATE, or NOT DEFERRABLE. The third class is always IMMEDIATE and is not affected by the SET CONSTRAINTS command. The first two classes start every transaction in the indicated mode, but their behavior can be changed within a transaction by SET CONSTRAINTS. lowkey neat.

SET CONSTRAINTS with a list of constraint names changes the mode of just those constraints (which must all be deferrable). Each constraint name can be schema-qualified. The current schema search path is used to find the first matching name if no schema name is specified. SET CONSTRAINTS ALL changes the mode of all deferrable constraints. periodt. 👑

When SET CONSTRAINTS changes the mode of a constraint from DEFERRED to IMMEDIATE, the new mode takes effect retroactively: any outstanding data modifications that would have been checked at the end of the transaction are instead checked during the execution of the SET CONSTRAINTS command. If any such constraint is violated, the SET CONSTRAINTS fails (and does not change the constraint mode). Thus, SET CONSTRAINTS can be used to force checking of constraints to occur at a specific point in a transaction. it’s giving “we’re doing this *now*” energy. 😭

Currently, only UNIQUE, PRIMARY KEY, REFERENCES (foreign key), and EXCLUDE constraints are affected by this setting. NOT NULL and CHECK constraints are always checked immediately when a row is inserted or modified (not at the end of the statement). Uniqueness and exclusion constraints that have not been declared DEFERRABLE are also checked immediately.

The firing of triggers that are declared as constraint triggers is also controlled by this setting — they fire at the same time that the associated constraint should be checked. iykyk 🔥

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🎀 NOTES 🎀

Because PostgreSQL does not require constraint names to be unique within a schema (but only per-table), it is possible that there is more than one match for a specified constraint name. In this case SET CONSTRAINTS will act on all matches. For a non-schema-qualified name, once a match or matches have been found in some schema in the search path, schemas appearing later in the path are not searched. fr fr, read that twice.

Heads up, bestie: this command only alters the behavior of constraints within the current transaction. Issuing this outside of a transaction block emits a warning and otherwise has no effect. So no transaction block = warning-only vibes. 💀

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👑 COMPATIBILITY 👑

This command complies with the behavior defined in the SQL standard, except for the limitation that, in PostgreSQL, it does not apply to NOT NULL and CHECK constraints. Also, PostgreSQL checks non-deferrable uniqueness constraints immediately, not at end of statement as the standard would suggest. And that’s the compatibility tea. 🍓

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Okay that’s the whole SET CONSTRAINTS(7) moment, bestie. This page is from the PostgreSQL 13.23 docs, dated 2025 — mwah, bye! 💋🫶