SQL 'select' 查询有 3 个条件

SQL 'select' Query with 3 conditions

提问by sanu j

SELECT * 
FROM REVIEW 
WHERE REVIEWERID =5 AND APPRAISEECONFIRMYN='Y' AND HRCONFIRMYN = NULL

Are 2 'AND' conditions allowed like this? I'm not getting the correct output. There are 2 records in the database that fulfil the above conditions. When I remove the last condition 'HRCONFIRMYN = NULL'and execute, I get the correct output.

像这样允许 2 个“AND”条件吗？我没有得到正确的输出。数据库中有 2 条记录满足上述条件。当我删除最后一个条件'HRCONFIRMYN = NULL'并执行时，我得到了正确的输出。

How can this be solved? I need to check all 3 conditions whilst searchng the records.

如何解决这个问题？我需要在搜索记录时检查所有 3 个条件。

回答by Mahmoud Gamal

To compare the NULLvalues, you have to use the IS NULLpredicate instead of = NULLlike so:

要比较这些NULL值，您必须使用IS NULL谓词而不是= NULL像这样：

SELECT * 
FROM REVIEW 
WHERE REVIEWERID = 5 
  AND APPRAISEECONFIRMYN = 'Y' 
  AND HRCONFIRMYN IS NULL

回答by John Woo

• use ORinstead
• group your condition
• use IS NULLwhen comparing with NULLs

• 使用OR替代
• 分组你的条件
• 使用IS NULL与空值进行比较时，

query,

询问，

SELECT * 
FROM REVIEW 
WHERE (REVIEWERID =5 AND APPRAISEECONFIRMYN='Y') OR
      HRCONFIRMYN IS NULL