9、SQL基础整理（两表连接exists,join on,union）

exists的用法

select *from haha where exists (select *from bumen where bumen.code = haha.bumen and bumen.name = '销售部' )and age>35

(运行方法为逐条查询)

select name,sex,age,(select name from bumen where bumen.code = haha.bumen)as 部门 from haha

select name,sex,age,(select name from bumen where bumen.code = haha.bumen)as 部门,(select ceo from bumen where bumen.code = haha.bumen)as ceo from haha

select haha.name,sex,age,bumen.name,ceo from bumen,haha where haha.bumen = bumen.code

2.join on（顺序可颠倒）

select haha.name,sex,age,bumen.name,ceo from haha

join bumen on haha.bumen = bumen.code

3.full的用法

insert into haha values(15,'实物','nv',34,5)

insert into bumen values(6,'保安部','保证安全',null,null)

select bumen.name,zhineng,ceo,haha.name,sex,age from haha

full join bumen on bumen.code = haha.bumen

4．left的用法

在没有关系的情况下，只显示join左边表的所有数据，不显示右边表的数据

5．right的用法

同上

（left 和right都是与所全部显示的数据的排序方式一致）

将两列连接起来，必须满足数据类型对应，具有自动去重的功能（按照拼音或者数字排列，打乱原有的顺序）

select*from haha where code > 10

union

select*from haha where code < 5

select name,bumen from haha where code > 10

union

select ceo,code from bumen