用union,举例有s1表(a,b,c,d)和s2表(a,c,d,e)和s3表(f,g),里头的字段不同,但在逻辑上有关系
(如有
s1.b=s2.e
s1.a=s3.f
s1.b=s3.g)
示例如下:
------------------------------------------------------------------------------
select
s1.a
as
x,s1.b
as
y,s1.c
as
z
from
s1
union
select
s2.a
as
x,s2.e
as
y,s2.c
as
z
from
s2
union
select
s3.f
as
x,s3.g
as
y,''
as
z
from
s3
------------------------------------------------------------------------------
最终结果会是三张表的和,如果s1有10条记录,s2有3条记录,s3有4条记录,则执行本sql后会得到17条记录,其中来自s3表的数据,第三列一定为空的。
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