SQL查询，计数和分组

Question

如果我有这样一组数据：

Key	Name
1	Dan
2	Tom
3	Jon
4	Tom
5	Sam
6	Dan

请问如何编写 SQL 查询语句，以筛选出 Name 字段重复两次或更多的记录呢？

即想要的结果为：

Tom
Dan

- Dan

Answer 1

再简单不过了...

Select Name, Count(Name) As Count 
    From Table
    Group By Name
    Having Count(Name) > 1
    Order By Count(Name) Desc

这也可以扩展到删除重复项：

Delete From Table
Where Key In (
    Select Max(Key)
        From Table
        Group By Name
        Having Count(Name) > 1
    )

- GateKiller

---

对于删除操作，您应该只保留Min(key)并删除其他条目。查询应修改为"...where Key NOT IN ( select Min(Key) ...." - aartist

Answer 2

select name from table group by name having count(name) > 1

- Ryan

Answer 3

这也可以通过将表与自身连接来实现，

SELECT DISTINCT t1.name
FROM    tbl t1
        INNER JOIN tbl t2
        ON      t1.name = t2.name
WHERE   t1.key         != t2.key;

- Dag Haavi Finstad