MySQL存储过程没有返回值

Question

如果我输入不同的值，它就会起作用。它返回了消息文本“该电子书不存在”的值

如果我输入数据库中的确切值，它只会执行但不会返回任何值。为什么？

CREATE PROCEDURE SPBus ( 
        IN BUS VARCHAR (20)
    )  
    BEGIN

    START TRANSACTION;
    IF  NOT EXISTS (SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS,'%' )) THEN
       SIGNAL SQLSTATE '45000'
       SET MESSAGE_TEXT= 'That ebook doesnt exists';
    ELSE 
        SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS, '%');
    END IF;
    COMMIT;
END;

Answer 1

因为当您没有设置 MESSAGE_TEXT 时，将执行该过程的 else 情况。试试这个:

CREATE PROCEDURE SPBus ( 
        IN BUS VARCHAR (20)
    )  
    BEGIN

    START TRANSACTION;
    IF  NOT EXISTS (SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS,'%' )) THEN
       SIGNAL SQLSTATE '45000'
       SET MESSAGE_TEXT= 'That ebook doesnt exists';
    ELSE 
        SELECT * FROM Ebook WHERE TituloEbook LIKE CONCAT('%',BUS, '%');
        SET MESSAGE_TEXT = 'That ebook exists';
    END IF;
    COMMIT;
END;