Instead of Comprueba = (SELECT "Usu_ID" FROM "Users" WHERE LOWER("Usu_Nick") = LOWER(xUsu_Nick) ); use SELECT "Usu_ID" INTO Comprueba FROM "Users" WHERE LOWER("Usu_Nick") = LOWER(xUsu_Nick) Rick
pgsql-bugs by date:
Соглашаюсь с условиями обработки персональных данных