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                            最近做項目寫sql的時候同時使用到了order by 和 group by.然而查詢出來的結果不是自己想象中的那樣.

下面來分析一樣原因: 
mysql 寫sql的順序: 
select -> from-> where->group by->having->order by. 
但mysql的解析器執行順序: 
from-> where->group by->having->select->order by. 
所以,從執行的流程來看,是先group by 然后在 order by. 
order by拿到的結果里已經是group by以后的結果.

因此,order by的字段必須是group by 里面已經存在的字段.

                    
                
        
                
            
        
                
    
                
    
                
        
                
    
                

                







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