Question

我在SQL中有DB2，并希望避免在第二个EXISTS中重复UNION子句中的条件，因为条件可能相当大。我怎么做？非常感谢任何帮助。

select id from table t where t.given_name = 'good' and t.time = 1 and exists
    (select 1 from table t1 where t1.id = t.id and t1.surname = 'OK') union
select id from table t where t.given_name = 'good' and t.time = 2 and not exists
    (select 1 from table t1 where t1.id = t.id and t1.surname = 'OK')

Answer 1

您为什么使用union？这样做怎么样？

select id
from table t
where t.given_name = 'good' and
      t.time in (1, 2) and
      exists (select 1 from table t1 where t1.id = t.id and t1.surname = 'OK');

如果id可能有重复项，请在外部查询中使用select distinct。＆＃39;

编辑：

我想我误解了原始查询。逻辑是：

select id
from table t
where t.given_name = 'good' and
      ( (t.time = 1 and exists (select 1 from table t1 where t1.id = t.id and t1.surname = 'OK')
        ) or
        (t.time = 2 and not exists (select 1 from table t1 where t1.id = t.id and t1.surname = 'OK')
        )
       )

Answer 2

我认为这也可以通过@Override public void setValueAt(Object aValue, int row, int column) { if (DEF.get(column).getValueSetterFunction() != null) { DEF.get(column).getObjectValueSetterFunction().accept(getObjectAt(row), aValue); } }子句

来实现

where

Answer 3

使用WITH子句删除冗余

with t2 as (select * from t1 where surname = 'OK')
select id from table t where t.given_name = 'good' and t.time = 1 and exists
    (select 1 from table t2 where t2.id = t.id) union
select id from table t where t.given_name = 'good' and t.time = 2 and not exists
    (select 1 from table t2 where t2.id = t.id) 
;

如果需要，你也可以对另一张表做同样的事情

with t2 as (select * from t1 where surname = 'OK')
,    tt as (select * from t  where given_name = 'good')
select id from table tt where tt.time = 1 and exists
    (select 1 from table t2 where t2.id = tt.id) union
select id from table tt where tt.time = 2 and not exists
    (select 1 from table t2 where t2.id = tt.id) 
;

如何避免在UNION中重复EXISTS子句中的条件

3 个答案: