SQL CASE子查询

Question

I have two tables, the following query to retrieve the os memory when max instance memory is unlimited and the error message:

--osmemory                          --instancememory
servername  osmemory                servername  instancename  instancememory
----------  --------                ----------  ------------  --------------
srva        4096                    srva        srva\insta    2048
srvb        6144                    srvb        srvb\instb    2147483647

select i.ServerName
     , i.instancename
     , case i.instance memory LIKE '2147483647' 
         then (select o.osmemory from o.osmemory
               join i.instance on o.servername = i.servername)
...

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

I've been trying (and i'm still trying) various scripts, but with no luck.

Can somebody help? Thanks

Answer 1

The error is obvious. You are using a subquery in a context where one column and up to one row is allowed. This is called a "scalar subquery". One method to fix this uses an aggregation function:

select i.ServerName, i.instancename,
       (case i.instance memory LIKE '2147483647' 
            then (select max(o.osmemory) from o.osmemory join i.instance on o.servername = i.servername)
       . . . 

However, that might not be your intent.

EDTI:

If I had to speculate, your problem is the join in the subquery. You probably just want a correlated subquery. This is a guess, but:

select i.ServerName, i.instancename,
       (case i.instance memory LIKE '2147483647' 
            then (select o.osmemory from o.osmemory where o.servername = i.servername)
       . . . 

Answer 2

还是使用Max（o.osmemory）或Max（o.osmemory）不管结果是否始终为1。