MySQL结果由存储过程中的多行组成

Question

我正在处理的存储过程有时会出错.我收到Result consisted of more than one row错误,但仅限于某些JOB_ID_INPUT值.我明白是什么导致了这个错误,所以我试着非常小心地确保我的返回值在它们应该是标量时.很难看到存储过程,所以我不确定可以在哪里生成错误.由于错误是有条件地抛出的,因此我认为内存可能是一个问题,或者游标重用.我不经常使用游标,所以我不确定.谢谢任何帮助过的人.

DROP PROCEDURE IF EXISTS export_job_candidates;
DELIMITER $$
CREATE PROCEDURE export_job_candidates (IN JOB_ID_INPUT INT(11))
BEGIN

DECLARE candidate_count INT(11) DEFAULT 0;
DECLARE candidate_id INT(11) DEFAULT 0;

# these are the ib variables
DECLARE _overall_score DECIMAL(5, 2) DEFAULT 0.0;

# declare the cursor that will be needed for this SP
DECLARE curs CURSOR FOR SELECT user_id FROM job_application WHERE job_id = JOB_ID_INPUT;

# this table stores all of the data that will be returned from the various tables that will be joined together to build the final export
CREATE TEMPORARY TABLE IF NOT EXISTS candidate_stats_temp_table (
    overall_score_ib DECIMAL(5, 2) DEFAULT 0.0
) engine = memory;

SELECT COUNT(job_application.id) INTO candidate_count FROM job_application WHERE job_id = JOB_ID_INPUT;

OPEN curs;

# loop controlling the insert of data into the temp table that is retuned by this function
insert_loop: LOOP

    # end the loop if there is no more computation that needs to be done
    IF candidate_count = 0 THEN 
        LEAVE insert_loop;
    END IF;

    FETCH curs INTO candidate_id;

    # get the ib data that may exist for this user
    SELECT
        tests.overall_score
    INTO 
        _overall_score
    FROM 
        tests
    WHERE
        user_id = candidate_id;

    #build the insert for the table that is being constructed via this loop 
    INSERT INTO candidate_stats_temp_table (
        overall_score
    ) VALUES (
        _overall_score
    );

    SET candidate_count = candidate_count - 1;

END LOOP;

CLOSE curs;

SELECT * FROM candidate_stats_temp_table WHERE 1;

END $$
DELIMITER ;

Answer 1

（WHERE 1正如 @cdonner 所指出的）看起来肯定不正确，但我很确定会发生此错误，因为您的SELECT ... INTO命令之一返回了不止一行。

这个应该没问题，因为它是一个没有 a 的聚合GROUP BY，它总是返回一行：

SELECT COUNT(job_application.id) INTO candidate_count
  FROM job_application WHERE job_id = JOB_ID_INPUT;

所以可能是这个：

# get the ib data that may exist for this user
SELECT
    tests.overall_score
INTO 
    _overall_score
FROM 
    tests
WHERE
    user_id = candidate_id;

尝试弄清楚此查询是否有可能返回多行，如果可以，您如何解决它。一种方法可能是MAX总分：

SELECT MAX(tests.overall_sore) INTO _overall_score
  FROM tests
  WHERE user_id = candidate_id