Question

I have two tables 

Table A       : 
                 Item    Lookup
                  A        X
                  B       null
                  C        Y
                  D        K

Table B       :   
                   Lookup
                     X
                     Y
                     Z

I want to join these tables and get output like 

              Item    Lookup
               A       X
               B       null
               C       Y

我想在输出视图中选择所有匹配的查找和空查找。任何人都可以告诉我加入条件

Answer 1

您希望B中的行与NULL匹配或inner join查找。您可以使用select distinct a.item, a.lookup from tableA a join tableB b on (a.lookup = b.lookup) or (a.lookup is NULL);和特殊条件执行此操作：

lookup

如果您有exists的索引，那么select a.item, a.lookup from tableA a where a.lookup is null or exists (select 1 from tableB b where b.lookup = a.lookup);的效果会更好：

left join

编辑：

也可以使用where select distinct a.item, a.lookup from tableA a left join tableB b on a.lookup = b.lookup where (a.lookup is NULL and b.lookup is NULL) or b.lookup is not null;条件：

<MY_JENKINS_INSTANCE>/git/notifyCommit?url=$CHANGED_REPOSITORY

Answer 2

以下查询将返回Lookup中TableB的{{1}}的所有记录，或NULL Lookup的所有记录：

SELECT Item, Lookup
FROM TableA
WHERE (Lookup IS NULL) OR Lookup IN (SELECT Lookup FROM TableB)

Answer 3

我认为这会有所帮助

SELECT DISTINCT A.Item, A.Lookup FROM A, B WHERE A.lookup=B.lookup OR A.lookup IS NULL

Answer 4

您也可以通过左外连接来执行此操作：

with tablea as (select 'A' item, 'X' lookup from dual union all
                select 'B' item, null lookup from dual union all
                select 'C' item, 'Y' lookup from dual union all
                select 'D' item, 'K' lookup from dual),
     tableb as (select 'X' lookup from dual union all
                select 'Y' lookup from dual union all
                select 'Z' lookup from dual)
select a.item,
       a.lookup
from   tableA a 
       left outer join tableB b on (a.lookup = b.lookup)
where  a.lookup is null
or     a.lookup = b.lookup;

ITEM LOOKUP
---- ------
A    X     
C    Y     
B

表加入条件

4 个答案: