Question

select case when integer=1 then (select col1,col2 from table1) 
            when integer=2 then (select col11,col22 from table2)
       end

子查询是否可以返回多个值，如果不是哪种方法比这更好？

Answer 1

CASE适用于标量而不是行。对于你的问题，我会用这个：

IF integer=1
  SELECT col1 AS colA, col2 AS colB FROM table1
ELSE IF integer=2
  SELECT col11 AS colA, col22 AS colB FROM table2

Answer 2

也许它不是特别干净，但这应该有效：

SELECT          CASE my_table.integer
                  WHEN 1 THEN table1.col1
                  ELSE        table2.col11
                END AS col_1,
                CASE my_table.integer
                  WHEN 1 THEN table1.col2
                  ELSE        table2.col2
                END AS col_2
FROM            my_table
LEFT OUTER JOIN table1
             ON ....
LEFT OUTER JOIN table2
             ON ....
...

Answer 3

您是否使用过MS Sql Server，如果是，您可以试试这个

declare @script nvarchar(400)
select @script = case SomeField -- conditions field
when 1 then 'select * from [TableA]'
when 2 then 'select * from [TableB]'
end
from [TableC] where ...
exec sp_executesql @script

但请注意将用户的任何输入连接到脚本。

Answer 4

您可以使用union all：

通过单个查询执行此操作

select col1, col2
from table1
where integer = 1
union all
select col1, col2
from table2
where integer = 2;

case语句中包含多个列的子查询

4 个答案: