mysql分組排序取最大值所在行,類似hive中row_number() over partition by
阿新 • • 發佈:2019-01-03
如下圖, 計劃實現 :按照 parent_code 分組, 取組中code最大值所在的整條記錄,如紅色部分。(類似hive中: row_number() over(partition by))
select c.* from ( select a.*, (@i := case when @key_i=parent_code then @i+1 else 1 end) as sort_num,(@key_i:=parent_code) as tmp from my_test a, (SELECT @i := 0,@key_i:='') border by parent_code,code desc) c where c.sort_num=1;
個人理解, mysql 執行順序: from >> where >> order by >> select .
以下部門應該有助於理解mysql中變數的概念。
1.=========================================================================================================
僅按照code排序,加序號sort_num效果如下:
select (@i := @i + 1) as sort_num, a.*
from my_test a, (SELECT @i := 0) b
order by code;
2.=========================================================================================================
僅按parent_code分組,按照code排序,加序號.
select a.*, (@i := case when @key_i=parent_code then @i + 1 else 1 end) as sort_num,(@key_i:=parent_code) as tmp
from my_test a, (SELECT @i := 0,@key_i:='') b
order by parent_code,code desc;
參考連結 :https://blog.csdn.net/zzhhoubin/article/details/79839610
https://www.cnblogs.com/CharlieLau/p/6737243.html
https://blog.csdn.net/u011728683/article/details/78594070