選擇每個項目的最後3行

Question

我有兩個表raw_materials和raw_materials_moves。

raw_materials有場

id, name 

raw_materials_moves有這個領域

id, raw_material_id, price, created 

所以，我需要每種原料的select最後3個移動

我有這樣的查詢，但doesn't工作

SELECT a.*, b.price, b.created 
FROM raw_materials a 
LEFT JOIN 
(SELECT price, raw_material_id, created FROM raw_material_moves ORDER BY created DESC LIMIT 3) b 
    ON b.raw_material_id=a.id 
ORDER BY a.id 

Answer 1

反向分類（即... SORT BY somefield DESC），然後獲得第3（通過附加LIMIT 3）

Answer 2

，我將通過創建

Answer 3

SELECT r1.id,name,raw_material_id 

FROM raw_materials r1, raw_materials_move r2 

WHERE r1.id=r2.id ORDER BY DESC LIMIT 3; 

Answer 4

最後3個移動以相反的順序獲取建議你到用戶光標DESC（或）（我假定日期）每種原料的

select * from 
    (select a.id,a.price,a.created, 
      if(@mat=a.raw_material_id,@num:=@num+1,@num:=1) rank, 
      @mat:=a.raw_material_id 
    from raw_materials_moves a, (select @num:=0) b 
    order by a.raw_material_id,a.created desc) temp 
where rank <=3; 

看到demo here

Answer 5

我會@chetan大多同意variabl的使用完成這項工作。

Here is one of the best articles我曾遇到過這方面的問題和不同的處理方法..從容易到難。