如何使用IF和ELSE语句进行sql查询

我有查询来选择获取答案值。我需要检查它是否应答或为空。我用（d.AM_Answer或null）它不起作用。它只取空值。所以，我改变了我的下面的查询，但它不工作。如何使用IF和ELSE语句进行sql查询

SELECT a.QM_ID, 
     a.QM_QCM_ID, 
     a.QM_Question, 
     a.QM_Type, 
     a.QM_Parent_Id, 
     c.AM_Answer, 
     c.AM_Comments 
FROM question_master a 
INNER JOIN Assessment_master c ON (c.AM_QM_ID = a.QM_ID 
            AND c.AM_HNM_ID = %d 
            AND c.AM_HM_ID = %d 
            AND c.AM_ASM_Local_Id = %@) 
WHERE a.QM_Parent_Id = 0 
    AND a.QM_Status = 'A' 
    AND a.QM_QCM_ID = %@ 
    AND a.QM_QRM_Id = %@ IF(d.AM_Answer IS NULL) THEN 
UNION 
SELECT b.QM_ID, 
     b.QM_QCM_ID, 
     b.QM_Question, 
     b.QM_Type, 
     b.QM_Parent_Id, 
     NULL, 
     NULL 
FROM question_master b 
INNER JOIN Assessment_master d ON ((d.AM_QM_ID = b.QM_Parent_Id 
            OR d.AM_QM_ID = b.QM_ID) 
            AND d.AM_HNM_ID = %d 
            AND d.AM_HM_ID = %d 
            AND d.AM_ASM_Local_Id = %@) 
WHERE b.QM_Parent_Id != 0 
    AND b.QM_Status = 'A' 
    AND b.QM_QCM_ID = %@ 
    AND b.QM_QRM_Id = %@ ELSE IF(d.AM_Answer IS NOT NULL) THEN 
UNION 
SELECT b.QM_ID, 
     b.QM_QCM_ID, 
     b.QM_Question, 
     b.QM_Type, 
     b.QM_Parent_Id, 
     d.AM_Answer, 
     d.AM_Comments 
FROM question_master b 
INNER JOIN Assessment_master d ON ((d.AM_QM_ID = b.QM_Parent_Id 
            OR d.AM_QM_ID = b.QM_ID) 
            AND d.AM_HNM_ID = %d 
            AND d.AM_HM_ID = %d 
            AND d.AM_ASM_Local_Id = %@) 
WHERE b.QM_Parent_Id != 0 
    AND b.QM_Status = 'A' 
    AND b.QM_QCM_ID = %@ 
    AND b.QM_QRM_Id = %@ END IF

来源

2014-02-27 user3351727

从http://dev.mysql.com/doc/refman/5.7/en/working-with-null.html：不能使用算术比较运算符（如=，<, or <>）来测试NULL。 – mcalex

@mcalex他可以使用IS NULL –

我猜它知道goves你的错误，因为联合关键字 –

1）要检查空值，可以使用COALESCE运算符。

2）您也可以使用SQL CASE语句

3）我建议你为你准备一个动态查询

来源

2014-02-27 05:42:31

哪里可以更改我的代码 – user3351727

您可以在查询中说明每个联合的目的吗？ –

使用存储过程，这个你可以把这里的条件d.answer是不为null以选择非空答案。

来源

2014-02-27 05:44:13 Cerberus

尝试

IF(d.AM_Answer IS null)

，而不是

IF(d.AM_Answer == null)

来源

2014-02-27 05:47:06 Prashant16

如何使用IF和ELSE语句进行sql查询

回答

相关问题