我有一个带有personid和msg colums的表.

personid, msg
--------------
 1,      'msg1'
 2,      'msg2'
 2,      'msg3'
 3,      'msg4'
 1,      'msg2'

我想获得每个personid的总消息.
我正在尝试这个查询：

select distinct personid, count(*)
FROM mytable;

我也试过这个查询

select distinct personid, count(msg)
FROM mytable;

但没有得到实际的结果.
我想要以上数据的结果：

id, count
--------
1,   2
2,   2
3,   1

解决方法:

您只需要使用GROUP BY而不是DISTINCT.所以试试这个查询：

SELECT personid, COUNT(msg) 
FROM mytable 
GROUP BY personid
ORDER BY personid;

See this SQLFiddle

GROUP BY lets you use aggregate functions, like AVG(), MAX(), MIN(),
SUM(), COUNT() etc while DISTINCT just removes duplicates.