PostgreSQL error code

PostgreSQL error 42723

42723 is the SQLSTATE PostgreSQL reports for duplicate function, in class 42, Syntax Error or Access Rule Violation.

SQLSTATE	42723
Condition name	duplicate_function
Class	42 — Syntax Error or Access Rule Violation

Reproduce it, then fix it

A function with that name and those argument types already exists. CREATE OR REPLACE swaps in the new body. Run the broken query to see the error, then switch to the fixed one. Edit either freely; every run is rolled back.

CREATE FUNCTION tax_rate() RETURNS numeric AS 'SELECT 0.20' LANGUAGE sql;
CREATE FUNCTION tax_rate() RETURNS numeric AS 'SELECT 0.19' LANGUAGE sql;

CREATE FUNCTION tax_rate() RETURNS numeric AS 'SELECT 0.20' LANGUAGE sql;
CREATE OR REPLACE FUNCTION tax_rate() RETURNS numeric AS 'SELECT 0.19' LANGUAGE sql;
SELECT tax_rate();

Source: PostgreSQL documentation, Appendix A