mysql
group by
SELECT ToQQ ,COUNT(Msg) AS msg //展现的列和数量
FROM `privatesendinformation` //表名
WHERE toqq='XXX' || toqq='XX2'
//如果有where一定加group by 前面
GROUP BY ToQQ
Join --->左连接
SELECT * FROM privatechatinformation LEFT JOIN privatesendinformation ON //两个表名
privatechatinformation.FromQQ=privatesendinformation.ToQQ; //对应变量名