union这个连接是有什么用的和INNERJOIN有什么区别

union这个连接是有什么用的和INNER JOIN有什么区别

Select A.Field1,B.field2 from Table1 A inner join Table2 B on a.Field2=b.Field2 where ..........
Select Field1 from Table1 union Select Field2 from table2
方案二、
select a.id,a.title,b.content from 表格1 as a,表格2 as b where a.id=b.id order by a.id

rs("id")
rs("title")
rs("content") 另：
新建一个表xxx

sql="insert into xxx select P.id,P.title,M.content from picture P inner join miaoshu M on P.id=M.id"
conn.execute sql