Question

有两张桌子：

[TableRule]
|RuleId (PK)|
|RuleDesc|
...

[TableRulesByUser]
|UserId|
...
|RuleId (FK)|

我希望使用额外的列检索所有TableRules，该列显示是否使用（引用）此RuleId。

我尝试过类似的事情：

select v.*,
            case
                when
                    (select count(b.RuleId) from TableRulesByUser b
                    join v on b.RuleId = v.RuleId  ) > 1
                    /* Here the join doesn't work */
                then 'Y' IsUsed
                else 'N' IsUsed
            end
    from TableRule v

Answer 1

尝试类似：

select 
v.*,
case when b.RuleId > 1
then 'y' 
else 'n' 
end
from tablerulesbyuser b
join tablerule v
on b.ruleid = v.ruleid
Group BY RuleDesc

Answer 2

SELECT
V.*,
CASE WHEN U.RuleID IS NULL THEN 'N' ELSE 'Y' END
FROM TABLERULES V
LEFT JOIN TABLERULESBYUSER U ON V.RuleID = U.RuleID

不确定PLSQL的语法是否正确，但想法是LEFT JOIN另一个表，如果没有使用，你将获得null，然后显示N，否则为Y.

如果在另一个表中引用行id，如何显示为列？

2 个答案: