怎么用sql语句,匹配多行数据的同一个字段

SQL code

create table mainTable
(
  mainId int
);

create table tagTable
(
  tagId int,
  tagName varchar(15)
);

create table relationTable
(
  mainId int,
  tagId int
);

基本结构就是这样了.mainTable是主数据表,tagTable是标签信息的数据表,relationTable记录mainTable的所有标签关系,单向的一对多关系.

能否利用sql语句,匹配同时包含某几个tagName的mainId

------解决方案--------------------
select mainId
from relationTable
where tagId in
(
select tagId from tagTable where tagName in ('A','B','C')
)
------解决方案--------------------
如果要找mainTable中数据，那么再套一层
select * from mainTable
where mainId
in
(
select mainId
from relationTable
where tagId in
(
select tagId from tagTable where tagName in ('A','B','C')
)
)