查询条件字段做运算优化

 

对字段做函数和运算完后无法使用索引。这么做的话，让优化器对字段产生歧义，不知道如何选择索引。因为这时候并没有一个concat(year_id,'-',month_id)这样的字段

 

   
   
   
   
    
    
    
    
    
  1. mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  concat(year_id,'-',if(month_id<10,'0',''),month_id)='2011-09'; 
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  3. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  5. | id | select_type | table                          | type | possible_keys | key  | key_len | ref  | rows    | Extra       | 
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  7. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  9. |  1 | SIMPLE      | mkt_order_by_month_userid_type | ALL  | NULL          | NULL | NULL    | NULL | 3673176 | Using where | 
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  11. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  13. 1 row in set (0.00 sec) 
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  17. mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  concat(year_id,'-',month_id)='2011-09'; 
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  19. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  21. | id | select_type | table                          | type | possible_keys | key  | key_len | ref  | rows    | Extra       | 
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  23. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  25. |  1 | SIMPLE      | mkt_order_by_month_userid_type | ALL  | NULL          | NULL | NULL    | NULL | 3673176 | Using where | 
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  27. +----+-------------+--------------------------------+------+---------------+------+---------+------+---------+-------------+ 
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  29. 1 row in set (0.00 sec) 
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优化方法，对要传入的值做函数操作

 

   
   
   
   
    
    
    
    
    
  1. mysql> explain select * from  data_market.mkt_order_by_month_userid_type where  year_id=substring('2011-09',1,4) and month_id = substring('2011-09',6,2); 
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  3. +----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+ 
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  5. | id | select_type | table                          | type | possible_keys | key     | key_len | ref         | rows   | Extra | 
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  7. +----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+ 
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  9. |  1 | SIMPLE      | mkt_order_by_month_userid_type | ref  | year_id       | year_id | 8       | const,const | 377128 |       | 
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  11. +----+-------------+--------------------------------+------+---------------+---------+---------+-------------+--------+-------+ 
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