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                            * 最左前綴匹配原則
* 不在索引列做運算或者使用函數；
* 盡量擴展索引，不要新增索引；比如已有a索引，需要新增(a,b)索引，建議修改a索引；
* where子句中經常使用的字段應該創建索引；分組字段或者排序字段應該創建索引；
* like模糊查詢中，右模糊查詢(321%)會使用索引，左模糊(%321和%321%)則會放棄索引使用全局掃描；
                    
                
        
                
            
        
                
    
                
    
                
        
                
    
                

                







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