mysql group by join（左连接）

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