Question

我试图使用计数器变量@row使用单个UPDATE / SELECT语句对桥表上的某些行进行编号。例如：

UPDATE teamrank JOIN (SELECT @row := @row + 1 AS position, name FROM members) 
       USING(teamID, memberID) SET rank = position

这样的事情是可能的还是我需要创建游标？如果有帮助，我正在使用MySQL 5.

Answer 1

- 始终初始化用户变量，否则默认为NULL。

SET @prevID:=@runSum:=0;

UPDATE teamrank t -- one row per team?
  JOIN members  m USING ( teamID ) -- multiple rows per team?
   SET rank =
IF( @prevID != m.teamID, /* Capture when a teamIDs changes */
    ( @runSum := m.rank ) + ((@prevID := m.teamID)*0), /* reset both @runSum and @prevTeam */
    ( @runSum := @runSum + m.rank) /* increment running sum */
  )
-- It is important to have proper sequencing, so to reset @runSum when a teamID changes.
ORDER BY t.teamID 
;

我假设执行团队排名所需的逻辑是团队中个人排名的总和。

同样的技术允许人们执行任何类型的运行总和或计数器，当“组”发生变化时需要重置。

- J Jorgenson -

Answer 2

如果我理解你的（不完整）查询，这应该会有所帮助：

UPDATE teamrank 
   JOIN (
      SELECT @row := @row + 1 AS position, name 
         FROM members, 
            (SELECT @row := 0) AS ObligatoryAlias
   ) USING(teamID, memberID) 
SET rank = position;

在SELECT语句中重置SQL变量

2 个答案: