我想用 FULL OUTER JOIN
在几个列的两个表之间,但是当两列都为空时,它们在连接过程中不被视为相等,因此我获得了两个不同的行。我如何编写我的连接,以便将空列视为相等?
我已经建立了一个简化的例子:
create table t1 (
id number(10) NOT NULL,
field1 varchar2(50),
field2 varchar2(50),
CONSTRAINT t1_pk PRIMARY KEY (id)
);
create table t2 (
id number(10) NOT NULL,
field1 varchar2(50),
field2 varchar2(50),
extra_field number(1),
CONSTRAINT t2_pk PRIMARY KEY (id)
);
insert into t1 values(1, 'test', 'test2');
insert into t2 values(1, 'test', 'test2', null);
insert into t1 values(2, 'test1', 'test1');
insert into t2 values(2, 'test1', 'test1', null);
insert into t1 values(3, 'test0', null);
insert into t2 values(3, 'test0', null, 1);
insert into t2 values(4, 'test4', 'test0', 1);
select *
from t1
full outer join t2 using (id, field1, field2);
得到的结果:
预期结果:
SQLFiddle
最佳答案
使用 NVL()和一个用于替换 NULL 的唯一字符串:
select t1.id,t1.field1,t1.field2,t2.extra_field
from t1
full outer join t2 ON
t1.id=t2.id
AND NVL(t1.field1,'UID_INSTEAD_OF_NULL')=NVL(t2.field1,'UID_INSTEAD_OF_NULL')
AND NVL(t1.field2,'UID_INSTEAD_OF_NULL')=NVL(t2.field2,'UID_INSTEAD_OF_NULL')
SQLFiddle demo
关于SQL : FULL OUTER JOIN on null columns,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32587083/