postgresql - 选择案例 : more than one row returned by a subquery used as an expression

Question

我的问题得到了很好的帮助 PostgreSQL: return message after count = 0

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表中有一些行，我需要显示选择结果。

我试过:

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

我得到了错误:

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

我发现了 IN 功能，但不知道如何改进它。

Answer 1

我认为你可以这样做:

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