--等值连接 select * from a,b where a.主键=b.主键 --左连接 select * from a left join b on a.主键=b.主键 --右连接 select * from a right join b on a.主键=b.主键
--同构纵向连接 select * from a union all select * from b--同构横向连接 select * from a join b on a.id=b.id --异构横向连接 select * from a join b on a.id=b.id--异构纵向连接,注意字段顺序. select *,null as 仅在b中存在的字段名 from a union all select *,null as 仅在a中存在的字段名 from b
select * from table1 where... union all select * from table2 where ....
select * from a,b where a.主键=b.主键
--左连接
select * from a left join b on a.主键=b.主键
--右连接
select * from a right join b on a.主键=b.主键
select * from a union all select * from b--同构横向连接
select * from a join b on a.id=b.id
--异构横向连接
select * from a join b on a.id=b.id--异构纵向连接,注意字段顺序.
select *,null as 仅在b中存在的字段名 from a union all select *,null as 仅在a中存在的字段名 from b
union all
select * from table2 where ....