数据库小积累
查看数据库执行sql语句优化
mysql> EXPLAIN EXTENDED
->
-> SELECT dept_name from course NATURAL JOIN section where `year` = 2009 GROUP BY dept_name HAVING COUNT(course_id) <= 1;
---- 结果----
+----+-------------+---------+------------+--------+-------------------+-------------+---------+------------------------------+------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+--------+-------------------+-------------+---------+------------------------------+------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | section | NULL | index | PRIMARY | section_fk2 | 28 | NULL | 100 | 10.00 | Using where; Using index; Using temporary; Using filesort |
| 1 | SIMPLE | course | NULL | eq_ref | PRIMARY,course_fk | PRIMARY | 10 | university.section.course_id | 1 | 100.00 | NULL |
+----+-------------+---------+------------+--------+-------------------+-------------+---------+------------------------------+------+----------+-----------------------------------------------------------+
2 rows in set, 2 warnings (0.00 sec)
mysql> show warnings ;
+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message |
+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1681 | 'EXTENDED' is deprecated and will be removed in a future release. |
| Note | 1003 | /* select#1 */ select `university`.`course`.`dept_name` AS `dept_name` from `university`.`course` join `university`.`section` where ((`university`.`course`.`course_id` = `university`.`section`.`course_id`) and (`university`.`section`.`year` = 2009)) group by `university`.`course`.`dept_name` having (count(`university`.`course`.`course_id`) <= 1) |
+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)数据库备份数据
# 只导出表结构
mysqldump -u root -p -d university > abc.sql
# 导出表结构以及数据
mysqldump -u root -p xx > abc.sql
# 导入数据
1、创建数据库
2、mysql -u root -p xx < abc.sql