檢查 query 語法是否能在 PostgreSQL 中執行，回傳 SQLSTATE

sqlcheck.sql

-- SELECT sqlcheck('select * from not_exist_table');
-- 42P01: undefined_table
-- SELECT sqlcheck('select * from not_exist_table wrong_syntax');
-- 42601: syntax_error
-- 語法檢查會優先於物件檢查

CREATE OR REPLACE FUNCTION sqlcheck(query text) RETURNS text AS
$$
DECLARE
	sql text;
	code text;
BEGIN
	code='00000';
	sql='EXPLAIN '||query;
	EXECUTE sql;
	RETURN code;

	EXCEPTION WHEN OTHERS THEN
		GET STACKED DIAGNOSTICS
			code=RETURNED_SQLSTATE;
			RETURN code;
END;
$$ language 'plpgsql';