mysql - 如何在不使用循环的情况下检查mysql游标结果为空

Question

我有一个返回 varchar 值的 mysql 函数。在这个函数中，我定义了一个仅给出单个值的游标。这意味着在我的 select 语句中，我使用表主键组合获取了特定值。因为我知道这个游标只返回一个值，所以我不想添加一个循环来检查游标是否返回一个值。

DELIMITER //
CREATE FUNCTION PROGRAM_API_Get_Name(
        program_id_     VARCHAR(15),
        uni_id_         VARCHAR(15),
        fac_id_         VARCHAR(15)) RETURNS VARCHAR(100)
BEGIN

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    DECLARE degree_name_ VARCHAR(100);

    DECLARE get_name_ CURSOR FOR
        SELECT program_name 
            FROM degree_program_tab
            WHERE program_id = program_id_
            AND   uni_id     = uni_id_
            AND   fac_id     = fac_id_;    

    OPEN get_name_;
    IF(!done) THEN
        FETCH get_name_ INTO degree_name_;
        CLOSE get_name_;
        RETURN degree_name_;
    END IF;

    RETURN NULL;

END//

这个函数给了我以下错误

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'BEGIN DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; ' at line 5 0.

如果你知道如何克服这个问题，请帮助我

Answer 1

我找到了这个问题的答案，

cursor.rowcount 是解决方案

DELIMITER //
CREATE FUNCTION PROGRAM_API_Get_Name(
        program_id_     VARCHAR(15),
        uni_id_         VARCHAR(15),
        fac_id_         VARCHAR(15)) RETURNS VARCHAR(100)
BEGIN

    DECLARE degree_name_ VARCHAR(100);

    DECLARE get_name_ CURSOR FOR
        SELECT program_name 
            FROM degree_program_tab
            WHERE program_id = program_id_
            AND   uni_id     = uni_id_
            AND   fac_id     = fac_id_;    

    OPEN get_name_;
    IF(get_name_.rowcount>0) THEN
        FETCH get_name_ INTO degree_name_;
        CLOSE get_name_;
        RETURN degree_name_;
    END IF;

    RETURN NULL;

END//