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使用procedure analyse()分析mysql_MySQL

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Release: 2016-05-30 17:11:03
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procedure analyse();语法如下

 

select column from table_name procedure analyse();

 

以下引用一段文章:

 

PROCEDURE ANALYSE 通过分析select查询结果对现有的表的每一列给出优化的建议。

PROCEDURE ANALYSE的语法如下:

 

SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max_elements,[max_memory]])

 

max_elements (默认值256) analyze查找每一列不同值时所需关注的最大不同值的数量.

analyze还用这个值来检查优化的数据类型是否该是ENUM,如果该列的不同值的数量超过了

max_elements值ENUM就不做为建议优化的数据类型。

max_memory   (默认值8192) analyze查找每一列所有不同值时可能分配的最大的内存数量

 

样例程序

------------------------------------------------------------------------------------
mysql> DESC user_account;
+-----------+------------------+------+-----+---------+----------------+
| Field     | Type             | Null | Key | Default | Extra          |
+-----------+------------------+------+-----+---------+----------------+
| USERID    | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| USERNAME  | varchar(10)      | NO   |     | NULL    |                |
| PASSSWORD | varchar(30)      | NO   |     | NULL    |                |
| GROUPNAME | varchar(10)      | YES  |     | NULL    |                |
+-----------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> select * from user_account PROCEDURE ANALYSE(1)\G;
*************************** 1. row ***************************
             Field_name: ibatis.user_account.USERID
              Min_value: 1
              Max_value: 103
             Min_length: 1
             Max_length: 3
       Empties_or_zeros: 0
                  Nulls: 0
Avg_value_or_avg_length: 51.7500
                    Std: 50.2562
      Optimal_fieldtype: TINYINT(3) UNSIGNED NOT NULL
*************************** 2. row ***************************
             Field_name: ibatis.user_account.USERNAME
              Min_value: dfsa
              Max_value: LMEADORS
.........................................................
---------------------------------------------------------------------------------------
Copy after login

 

从第一行输出我们可以看到analyze分析ibatis.user_account.USERID列最小值1,最大值103,最小长度1,

最大长度3...,并给出了改字段的优化建议:建议将该字段的数据类型改成TINYINT(3) UNSIGNED NOT NULL。

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