返回多行时带有 case 的 sql 查询

Question

我正在尝试使用 case when 条件进行查询以查看我将显示的列表，但我遇到此错误 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

是否可以在 case 条件中调用多行查询？

Answer 1

我会分多个步骤执行此操作。获取操作类型，然后发出适当的查询。您是在前端还是在存储过程中使用此逻辑由您决定，并且可能取决于很多其他因素。

如果你绝对需要这样做，那么你可以尝试这样的事情:

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