SELECT CASE：用作表达式的子查询返回多行

Question

我的问题得到了很好的帮助

这个查询工作正常：

SELECT  CASE WHEN COUNT(*)  = 0 THEN 'NO RESULT'
            ELSE CAST(COUNT(*) as TEXT)
        END as myfield from mytable

但是今天我需要如果某些行在 table 中，我需要显示 select 结果。

我试过了：

SELECT  CASE WHEN COUNT(*)  = 0 THEN 'NO RESULT'
             ELSE (select name from mytable)
        END as myfield from mytable

我得到错误：

ERROR: more than one row returned by a subquery used as an expression

我发现 IN 功能，但不知道如何改进它。

Answer 1

我想你可以这样做：

select name from mytable
UNION ALL
SELECT 'NO RESULT'
WHERE NOT EXISTS(SELECT NULL FROM mytable)

SELECT CASE: more than one row returned by a subquery used as an expression