與

Question

列

分組遞增的值更新表我有一個自我引用表在MySQL

Posts 
postId 
FK_PostId 
idx 

的IDX值目前0，但我需要更新他們讓每一個有帖子ID每FK_PostId的遞增值。簡單地說，但非功能寫成

update idx = idx + 1 where FK_PostId is not null order by postId group by FK_PostID 

期望的結果

postId 15 FK_PostId 4 idx 0 
postId 16 FK_PostId 4 idx 1 
postId 17 FK_PostId 4 idx 2 
postId 18 FK_PostId 4 idx 3 
postId 24 FK_PostId 4 idx 4 
postId 32 FK_PostId 50 idx 0 
postId 35 FK_PostId 50 idx 1 

我似乎無法扎堆智能查詢此。 任何人都可以幫我嗎？

Answer 1

這似乎這樣的伎倆

UPDATE WallPost p, 

( SELECT @r:= IF(@u = FK_PostID, @r + 1,0) AS ROWNUM, 
       postID, 
       FK_PostID, 
       @u:= FK_postID 
     FROM WallPost, 
       (SELECT @i:= 1) AS r, 
       (SELECT @u:= 0) AS u 
     WHERE FK_PostID is not null 
     ORDER BY FK_PostID, idx, postID 
    ) AS s 
set p.idx = s.ROWNUM 
where p.postId = s.postId; 

基於位置的解決方案： query to add incremental field based on GROUP BY

Answer 2

mysql> set @f := null; 
mysql> UPDATE Posts 
    SET 
     idx = IF(FK_postId = @f, @i := @i+1, @i := 1), 
     FK_postId = (@f := FK_postId) 
    ORDER BY FK_postId, postId;