Sql的一些记录

有些sql语句需要用到时总不知道怎么写，开个博客记下来。

1.获取最近X天的数据

select * from points_order_info where datediff(now(), server_time) < X

文档：

 DATEDIFF(expr1,expr2)

DATEDIFF() returns expr1 – expr2 expressed as a value in days from one date to the other. expr1 and expr2are date or date-and-time expressions. Only the date parts of the values are used in the calculation.

mysql> SELECT DATEDIFF('2007-12-31 23:59:59','2007-12-30');
        -> 1
mysql> SELECT DATEDIFF('2010-11-30 23:59:59','2010-12-31');
        -> -31

2.索引

查看所有

show index from tablename

show keys from tablename

创建索引

CREATE INDEX index_name ON table_name (column_list)

删除索引

DROP INDEX index_name ON talbe_name