如下表：
表名：Test
| ID | RowID | Col1 | Col2 |
| 1 | 1 | A | A |
| 2 | 1 | B | A |
| 3 | 1 | A | B |
| 4 | 1 | C | B |
1,查找表中字段重复的只查找一次
select distinct Col1 from Test ;
select Col1 from Test where ID in(select min(ID) from Test group by Col1 );
结果为：
A
B
C
2，统计并查询该字段出现的数量
SELECT Col1,COUNT(Col1) FROM Test GROUP BY Col1;
结果为：
A 2
B 1
C 1
3，把一列多行内容拼成一行
select STUFF ((select ','+F.Col1 from Test F where F.RowID= 1 order by F.ID FOR XML PATH('')),1,1,'') As Col3;
结果为：
Col3
A,B,A,C