Tips for MySQL _ MySQL

Some MySQL skills Use RAND () to obtain random results

In the order by statement, you can retrieve data rows in the following random ORDER:

Mysql> SELECT * FROM tbl_name order by rand ();

Combination of order by rand () and LIMIT it is useful to select random samples from a group of columns:

Mysql> SELECT * FROM table1, table2 WHERE a = B AND c

-> Order by rand () LIMIT 1000;

Group by column alias

The data table does not have the day field (date type) and only has the ctime field (datetime type). However, daily summary statistics are required:

Mysql> select date (ctime) as day, count (*) from league_apply where ctime> = '2017-02-15 'and ctime <= '2017-02-28' group by day;