Question

抱歉，不清楚。我的当前查询如下所示，除了某些条件外，工作正常。

SELECT A.*, 
(SELECT .... from Emp where name = A.Name...... ) 
(SELECT .... from Emp where name = A.Name...... ) 
    ........
FROM (SELECT DISTINCT column1, column2, column3 
FROM xxx 
WHERE condition1) A

有时，下面的查询，即from子句中没有给出结果。

SELECT DISTINCT column1, column2, column3 
FROM xxx 
WHERE condition1

如果上述子查询没有结果，我不希望以下查询因加入而失败

(SELECT .... from Emp where name = A.Name...... ) 
(SELECT .... from Emp where name = A.Name...... )

当来自from cause的子查询没有返回结果时，显示Emp表中的所有内容而没有连接，即没有名称= A.Name
当来自from cause的子查询返回结果时，然后在Emp表中显示所有连接，即名称= A.Name

因此，尝试添加case语句如下，以检查子查询是否给出任何结果。也许有更好的方法来实现这一目标。

请就此提供帮助。

SELECT A.*, 
CASE WHEN exists (select A.*) THEN 
    (SELECT .... from Emp where condition 1...... ) 
WHEN not exists (SELECT A.*) THEN 
    (SELECT .... from Emp where condition 2...... ) 
END Column_Dummy 
FROM (SELECT DISTINCT column1, column2, column3 
FROM xxx 
WHERE condition1) A

根据我在下面尝试给出的建议，我收到错误，因为无效的对象名称＆＃39; A＆＃39;

SELECT A.* 
CASE WHEN (SELECT COUNT(*) FROM A Where ....) = 0 THEN 'not result'       
ELSE 'you have something there '
END

Answer 1

使用COUNT(*)

的查询

 SELECT A.*
       CASE WHEN (SELECT COUNT(*) FROM Table Where ....) = 0 THEN `not result`
            ELSE `you have something there`
       END

SQL Server嵌套select in from子句

1 个答案: