如何在存储过程 WHERE 子句中使用 IF/CASE 语句答案

【问题标题】：How to use IF/CASE statement in stored procedure WHERE clause如何在存储过程 WHERE 子句中使用 IF/CASE 语句
【发布时间】：2017-08-18 07:09:35
【问题描述】：

我有这样的存储过程

DELIMITER $$

DROP PROCEDURE IF EXISTS `shashiTest`$$

CREATE DEFINER=`user`@`%` PROCEDURE `shashiTest`(IN GroupId INT, IN UserId INT, IN ChapterId INT)
BEGIN
    select 
    sum(qptdq.mark)-sum(qpe.marks) as marks_detucted,
    count(qpe.tc_question_message_type_id) AS noof_errors,
    (SELECT tqmt.key_value from tc_question_message_type tqmt WHERE tqmt.id=qpe.tc_question_message_type_id) AS error_type
    from question_paper qp
    INNER JOIN question_paper_group_student_map qpgsm ON qpgsm.question_paper_id=qp.id
    INNER JOIN institute_group_student_map igsm ON igsm.id=qpgsm.institute_group_student_map_id AND igsm.group_id=GroupId AND igsm.user_id=UserId
    INNER JOIN question_paper_template_detail qptd ON qptd.question_paper_template_id=qp.question_paper_template_id
    INNER JOIN question_paper_template_detail_question qptdq ON qptdq.question_paper_template_detail_id=qptd.id
    INNER JOIN question_paper_details qpd ON qpd.question_paper_template_detail_question_id=qptdq.id AND qpd.question_paper_id=qp.id
    INNER JOIN tc_question_mapping tcm ON tcm.tc_question_id=qpd.question_id
    INNER JOIN question_paper_evaluation qpe ON qpe.child_question_id=qptdq.id AND qpe.user_id=30 AND qpe.question_paper_id=qp.id AND qpe.tc_question_message_type_id IS NOT NULL
    INNER JOIN topic t ON t.cms_id=tcm.syllabus_chapter_details_id
    INNER JOIN chapter c ON c.id=t.chapter_id   
    IF (ChapterId IS NOT NULL)  THEN
        WHERE qp.question_paper_status_id >= 7 and c.id = ChapterId
    ELSE
        WHERE qp.question_paper_status_id >= 7
    END IF;
    GROUP BY qpe.tc_question_message_type_id LIMIT 5;
    END$$

DELIMITER ;

我想根据我的参数添加 where 条件，因为我有一个可选参数。 问题：我没有正确的语法。我怎样才能做到这一点。请帮忙。谢谢。

【问题讨论】：

标签： mysql database stored-procedures

【解决方案1】：

DELIMITER $$

DROP PROCEDURE IF EXISTS `shashiTest`$$

CREATE PROCEDURE `shashiTest`(IN GroupId INT, IN UserId INT, IN ChapterId INT)
BEGIN
    select 
    sum(qptdq.mark)-sum(qpe.marks) as marks_detucted,
    count(qpe.tc_question_message_type_id) AS noof_errors,
    (SELECT tqmt.key_value from tc_question_message_type tqmt WHERE tqmt.id=qpe.tc_question_message_type_id) AS error_type
    from question_paper qp
    INNER JOIN question_paper_group_student_map qpgsm ON qpgsm.question_paper_id=qp.id
    INNER JOIN institute_group_student_map igsm ON igsm.id=qpgsm.institute_group_student_map_id AND igsm.group_id=GroupId AND igsm.user_id=UserId
    INNER JOIN question_paper_template_detail qptd ON qptd.question_paper_template_id=qp.question_paper_template_id
    INNER JOIN question_paper_template_detail_question qptdq ON qptdq.question_paper_template_detail_id=qptd.id
    INNER JOIN question_paper_details qpd ON qpd.question_paper_template_detail_question_id=qptdq.id AND qpd.question_paper_id=qp.id
    INNER JOIN tc_question_mapping tcm ON tcm.tc_question_id=qpd.question_id
    INNER JOIN question_paper_evaluation qpe ON qpe.child_question_id=qptdq.id AND qpe.user_id=30 AND qpe.question_paper_id=qp.id AND qpe.tc_question_message_type_id IS NOT NULL
    INNER JOIN topic t ON t.cms_id=tcm.syllabus_chapter_details_id
    INNER JOIN chapter c ON c.id=t.chapter_id   
    WHERE
    CASE WHEN ChapterId IS NOT NULL THEN  //<---I had made changes at this line
         qp.question_paper_status_id >= 7 and c.id = ChapterId
    ELSE
       qp.question_paper_status_id >= 7
    END
    GROUP BY qpe.tc_question_message_type_id LIMIT 5;
    END$$

DELIMITER ;

你可以试试上面的代码。

我已经添加了CASE WHEN。

【讨论】：

【解决方案2】：

IF (ChapterId IS NOT NULL)  THEN
    WHERE qp.question_paper_status_id >= 7 and c.id = ChapterId
ELSE
    WHERE qp.question_paper_status_id >= 7
END IF;

你可以改写成

WHERE qp.question_paper_status_id >= 7
  AND (c.id = ChapterId OR ChapterId IS NULL)

这里不需要 IF 或 CASE 语句。

【讨论】：