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PostgreSQL error code

PostgreSQL error P0001

P0001 is the SQLSTATE PostgreSQL reports for raise exception, in class P0, PL/pgSQL Error.

SQLSTATEP0001
Condition nameraise_exception
ClassP0 — PL/pgSQL Error

Reproduce it, then fix it

P0001 is the code for RAISE EXCEPTION when no other code is given, so the message comes from your own function or trigger. Here reserve_stock refuses to reserve more than is in stock. Run the broken query to see the error, then switch to the fixed one. Edit either freely; every run is rolled back.

SELECT reserve_stock(2, 500);
SELECT reserve_stock(2, 5);

Source: PostgreSQL documentation, Appendix A