SQL查询与一个案件，当返回多个行

Question

我试图做一个案件的查询条件，看看我会显示什么列表，但我有这个错误ORA-01427: single-row subquery returns more than one row。

查询是这样的：

select 
CASE WHEN action_type like 'Trigger Severity' THEN (select cast(SEVERITY as varchar2(255)) name from SURV_TRIGGER_SEVERITY_LIST) 
    WHEN action_type like 'Host Group' then (select cast(name as varchar2(255)) name from Surv_List.groups) 
    WHEN action_type like 'Host' then (select cast(name as varchar2(255)) name from tn_tree) 
    END display_value 
from surv_action_type_list 
where id = 0 

是possibel调用查询更多一行的情况下，条件里面？

Answer 1

我会在多个步骤做到这一点。获取操作类型，然后发出适当的查询。无论你是在前端还是在存储过程中都有这个逻辑，你就可能会依赖于很多其他的东西。

如果你绝对需要做这种方式，那么你可以尝试这样的事：

SELECT 
    SQ.display_value 
FROM 
    surv_action_type_list SATL 
INNER JOIN 
    (
    SELECT 
     'Trigger Severity' action_type, 
     CAST(severity AS VARCHAR2(255)) display_value 
    FROM 
     SURV_TRIGGER_SEVERITY_LIST 
    UNION ALL 
    SELECT 
     'Host Group' action_type, 
     CAST(name AS VARCHAR2(255) display_value 
    FROM 
     Surv_List.groups 
    UNION ALL 
    SELECT 
     'Host' action_type, 
     CAST(name AS VARCHAR2(255) display_value 
    FROM 
     tn_tree 
    ) SQ ON 
    SQ.action_type = SATL.action_type 
WHERE 
    SATL.id = 0 

Answer 2

您有3个子查询。

1. select cast(SEVERITY as varchar2(255)) name from SURV_TRIGGER_SEVERITY_LIST 
2. select cast(name as varchar2(255)) name from Surv_List.groups 
3. select cast(name as varchar2(255)) name from tn_tree 

每一个必须返回0或1行，但不是更多。

Answer 3

不可以。您的子查询应该只返回一个值（只有一行和一列），因为您将在单行中显示它。

由于您使用上面的查询将值显示为一列，所以您的意图看起来像只有一个值。

select 
CASE WHEN action_type like 'Trigger Severity' THEN (select cast(SEVERITY as varchar2(255)) name from SURV_TRIGGER_SEVERITY_LIST) 
    WHEN action_type like 'Host Group' then (select cast(name as varchar2(255)) name from Surv_List.groups) 
    WHEN action_type like 'Host' then (select cast(name as varchar2(255)) name from tn_tree) 
    END display_value 
from surv_action_type_list 
where id = 0 

有没有一个地方缺少的链接这个ID来说一个严重性列表？ 通常查询这样会在子查询的条件..像..

select 
    CASE WHEN action_type like 'Trigger Severity' 
      THEN (select cast(SEVERITY as varchar2(255)) name 
         **from SURV_TRIGGER_SEVERITY_LIST trglst 
         where trglst.name = lst.severity_name** 
    ----- 
    --- 

     END display_value 
    from surv_action_type_list lst 
    where id = 0