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                            ## **SQL的優化方案**
* 選用合適的字段
* 表連接代替子查詢
* limit 分布優化，先利用ID定位，再分頁
*  or條件優化，多個or條件可以用union all對結果進行合并（union all結果可能重復） 
* 不必要的排序 
* where代替having,having 檢索完所有記錄，才進行過濾
*  避免嵌套查詢
*  對多個字段進行等值查詢時，聯合索引


                    
                
        
                
            
        
                
    
                
    
                
        
                
    
                

                







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