触发器内的If语句不工作SQL(Oracle)

我的目标是创建一个触发器,检查您试图输入的数字 NR_RECIBO 在桌子上 Doc_cabecalho 具有属性 TIPO_DOC = 4

CREATE OR REPLACE TRIGGER ValidaRecibo
BEFORE INSERT ON Recibo
FOR EACH ROW
DECLARE val NUMBER;
BEGIN
    SELECT COUNT(*) INTO val 
    FROM Doc_cabecalho 
    WHERE (TIPO_DOC = 4 AND NR_DOCUMENTO = :NEW.NR_RECIBO);

    IF val = 0 
    THEN (-20502, ' Only from department 4 ');
    END IF;
END ValidaRecibo;

然而,这会引发以下错误:

PLS-00103:遇到符号“,”,但应为以下之一:
*=-+</>at in是mod余数而不是rem<>或!=或~=>=<=<(lt;)>和或like like 2 like 4 like c as between | member submultiset