本篇内容介绍了“怎么使用MySQL的Query-rewrite”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！

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1 启用或禁用

1. /usr/local/mysql/bin/mysql -uroot -p`cat /etc/sqlpass ` -P3306 -h227.0.0.1 < $BASEDIR/share/install_rewriter.sql

2. /usr/local/mysql/bin/mysql -uroot -p`cat /etc/sqlpass ` -P3306 -h227.0.0.1 < $BASEDIR/share/uninstall_rewriter.sql 

3.  

4. mysql> show variables like 'rewrite_%';
   +------------------+-------+
   | Variable_name    | Value |
   +------------------+-------+
   | rewriter_enabled | ON    |
   | rewriter_verbose | 1     |
   +------------------+-------+

5. mysql> use query_rewrite;
   mysql> show tables;
   +-------------------------+
   | Tables_in_query_rewrite |
   +-------------------------+
   | rewrite_rules           |
   +-------------------------+
   1 row in set (0.00 sec)
   
   [mysqld]
   rewriter_enabled=ON

2 简单练习

1. mysql> insert into rewrite_rules(pattern,pattern_database,replacement) values('select ?','test','select ?+1');
   mysql> call flush_rewrite_rules();

2. mysql> select 1;
   +-----+
   | 1+1 |
   +-----+
   |   2 |
   +-----+
   

3 去除类型转换

1. mysql> show create table tb\G;
   *************************** 1. row ***************************
          Table: tb
   Create Table: CREATE TABLE `tb` (
     `id` int(10) DEFAULT NULL,
     `name` varchar(20) DEFAULT NULL,
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8
   
   
   mysql> select * from tb;
   +------+----------+
   | id   | name     |
   +------+----------+
   |    1 | 12345678 |
   |    1 | 12345671 |
   |    1 | 12345672 |
   |    1 | 12345673 |
   |    1 | 12345674 |
   |    1 | 12345675 |
   |    1 | 12345676 |
   |    1 | 12345677 |
   |    1 | 12345679 |
   +------+----------+

mysql> explain select * from tb where name=12345677;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | tb    | NULL       | ALL  | idx_name      | NULL | NULL    | NULL |    9 |    11.11 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+

mysql> insert into rewrite_rules(pattern,pattern_database,replacement) values("select * from tb where name=?","test","select * from tb where name = cast(? as char character set utf8)");
Query OK, 1 row affected (0.08 sec)
思考：为什么不直接写？替换为‘？’ ，因为？如果被单引号包起来就失效了！

mysql> call flush_rewrite_rules();
Query OK, 0 rows affected (0.09 sec)

mysql> select * from tb where name=12345678;
mysql> show warnings;
+-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                       |
+-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1105 | Query 'select * from tb where name=12345678' rewritten to 'select * from tb where name = cast(12345678 as char character set utf8)' by a query rewrite plugin|
+-------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

4 改字段名后兼容报错

1. 
   
   mysql> select * from tb where uid=1;
   ERROR 1054 (42S22): Unknown column 'uid' in 'where clause'

2. mysql> insert into rewrite_rules(pattern,pattern_database,replacement) values("select * from tb where uid=?","test","select * from tb where id=?");
   Query OK, 1 row affected (0.06 sec)
   
   mysql> call flush_rewrite_rules();
   Query OK, 0 rows affected (0.06 sec)

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