MySQL：將每組的前N行插入表中。假設百萬組

Question

這樣做對一組很簡單：

INSERT INTO top_dancers_by_group 
    SELECT group_id, dancer_id 
    FROM dancers 
    WHERE group_id = 1 
    ORDER BY how_good_they_do_a_half_turn DESC 
    LIMIT 1000 

現在讓我們假設有一個groups表，包括數千組ID。如何在純MySQL中爲每個組標識執行此插入操作？

Answer 1

我會用一個存儲過程：

delimiter $$ 
create procedure insert_top_dancers_by_group() 
begin 
    declare gId int; 
    declare done tinyint default 0; 
    declare curGroup cursor for 
     select distinct group_id from dancers; 
    declare continue handler for not found 
     set done = 1; 

    open curGroup; 
    group_insert: while done=0 do 
     fetch curGroup into gId; 
     if done = 0 then 
      -- If you want to remove the previous stored dancers for this group: 
      delete from top_dancers_by_group where group_id = gId; 
      -- Insert the top dancers for this group: 
      insert into top_dancers_by_group 
       select group_id, dancer_id 
       from dancers 
       where group_id = gId 
       order by how_good_they_do_a_half_turn DESC 
       limit 1000; 
     end if; 
    end while; 
    close curGroup; 
end $$ 
delimiter ; 

希望這有助於。

---

您還可以使用參數在此過程中，以確定有多少行被插入：

delimiter $$ 
create procedure insert_top_n_dancers_by_group(n int) 
begin 
    declare gId int; 
    declare done tinyint default 0; 
    declare curGroup cursor for 
     select distinct group_id from dancers; 
    declare continue handler for not found 
     set done = 1; 

    open curGroup; 
    group_insert: while done=0 do 
     fetch curGroup into gId; 
     if done = 0 then 
      -- If you want to remove the previous stored dancers for this group: 
      delete from top_dancers_by_group where group_id = gId; 
      -- Insert the top dancers for this group: 
      insert into top_dancers_by_group 
       select group_id, dancer_id 
       from dancers 
       where group_id = gId 
       order by how_good_they_do_a_half_turn DESC 
       limit n; 
     end if; 
    end while; 
    close curGroup; 
end $$ 
delimiter ; 

一旦你創建的程序（一個或多個），你可以打電話給他們這樣的：

call insert_top_dancers_by_group();