PostgreSQL not_null_violation (Error 23502) – Causes and Fixes

What is PostgreSQL Error 23502 (not_null_violation)?<\/h3>Error 23502 signals that a statement attempted to insert or update a NULL into a column that carries the NOT NULL constraint. PostgreSQL blocks the write to protect data integrity and returns this exception to the client.<\/p>

The violation can surface in plain DML, inside triggers, functions, COPY operations, or even INSERT ... SELECT statements.

Fixing it quickly is critical because the transaction that raised the error is aborted, leaving no partial data written.<\/p>

What Causes This Error?<\/h3>Most cases stem from missing columns in an INSERT list, supplying explicit NULL, or forgetting to return a non-NULL value in a trigger function.

Automatic processes such as default values that resolve to NULL or generated columns that evaluate to NULL can also trigger the exception.<\/p>

Developers frequently hit the error after adding a NOT NULL constraint to an existing table without backfilling data, or when refactoring schemas and overlooking application code paths that now write NULLs.<\/p>

How to Fix PostgreSQL Error 23502<\/h3>First, identify the failing column in the server message.

Add the required non-NULL value in the INSERT or UPDATE, or populate a DEFAULT that evaluates to a valid value. If NULLs are acceptable, ALTER TABLE ... DROP NOT NULL or make the column nullable.<\/p>

When the error arises from a trigger or function, adjust the PL\/pgSQL code to ensure the NEW record returns a value for every NOT NULL column before issuing RETURN NEW.<\/p>

Common Scenarios and Solutions<\/h3>Bulk imports via COPY often omit columns.

Provide column lists and defaults to prevent NULL insertion. Upserts using INSERT ... ON CONFLICT may update a row to NULL; guard with COALESCE in the SET clause. Generated identity columns fail when overridden with NULL; omit the column from the statement.<\/p>

After adding NOT NULL to an existing column, run UPDATE table SET col = fallback WHERE col IS NULL; before enforcing the constraint to avoid runtime failures.<\/p>

Best Practices to Avoid This Error<\/h3>Always declare sensible DEFAULT values for mandatory columns.

Validate payloads in the application layer. Use CHECK constraints for complex rules, and add NOT NULL only after cleansing legacy data. Continuous integration tests catching NULL writes help catch regressions early.<\/p>

Galaxy’s SQL editor highlights NOT NULL definitions in its schema sidebar and its AI copilot warns when a query omits required columns, reducing the odds of runtime violations.<\/p>

Related Errors and Solutions<\/h3>Error 23514 (check_violation) occurs when a CHECK constraint fails and is fixed by satisfying the predicate or relaxing the rule.

Error 23505 (unique_violation) fires on duplicate keys; resolve it by deduplicating data or altering index strategy. Error 23503 (foreign_key_violation) happens when a referenced row does not exist; insert the parent row or remove the orphan record.<\/p>

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