SQL查询语句

三表联查语句

$sql = “select a.,b.,c* from (tableA a LEFT JOIN table b ON a.字段=b.字段) LEFT JOIN tableC c ON c.字段=b.字段或者a.字段 where 条件”；

SQL按时间段group by

按小时分组

SELECT COUNT(*),FROM_UNIXTIME(dt) FROM sub_date GROUP BY FROM_UNIXTIME(dt, ‘%Y-%m-%d %H’)

按分钟分组

SELECT COUNT(*),FROM_UNIXTIME(dt) FROM sub_date GROUP BY FROM_UNIXTIME(dt, ‘%Y-%m-%d %H:%i’)

按天分组

SELECT COUNT(*),FROM_UNIXTIME(dt) FROM sub_date GROUP BY FROM_UNIXTIME(dt, ‘%Y-%m-%d’)

三表联删语句

DELECT t1,t2,t3 FROM t1,t2,t3 WHERE t1.id=t2.id and t1.id=t3.id and t2.id=t3.id and 条件