mysql选择行号查询

Question

我在尝试根据表的某些子集中的（upvotes-downvotes）选择行号时遇到此查询的麻烦，但我还需要在同一查询中重置@rownum：

该查询有效，但我需要运行其中两个。 无论如何将集合@rownum组合成一个查询，我的尝试都是徒劳的。

SET @rownum = 0;
SELECT rank  
FROM (SELECT *, @rownum:=@rownum + 1 AS 
rank FROM Cars where Auto_SET = 'BMW'
order by (upvotes-downvotes) DESC) d
WHERE ID = 391802

这引发了一个错误：

SELECT rank 
FROM (SELECT *, @rownum:=@rownum + 1 AS 
rank FROM Cars  where Auto_SET = 'BMW' , 
(SELECT @rownum:=0) r order by 
(upvotes-downvotes) DESC) d
WHERE ID = 391913

Answer 1

cross-join应与select from table_name的select from table_name一起使用，例如

SELECT rank 
FROM (
  SELECT *, 
  @rownum:=@rownum + 1 AS rank 
  FROM Cars ,(SELECT @rownum:=0) r 
  where Auto_SET = 'BMW' 
  order by 
 (upvotes-downvotes) DESC
) d
WHERE ID = 391913

Answer 2

这样的事情也应该起作用：

SELECT @rn := @rn+1 AS RANK,t1.* FROM (

 # Your query here.
 SELECT * FROM Cars WHERE Auto_SET = 'BMW' 
 WHERE ID = 391913 ORDER BY (upvotes-downvotes) DESC

) t1, (SELECT @rn:=0) t2;

祝好运！！