mysql - 如何让MySQL知道顺序查询引起的ID？

Question

在下面的查询中，“id1”和“id2”都是未知的，无论我将它们更改为“myTable.id1”或“r1.id1”或“r2.id1”:

SELECT      @n:=@n+1 AS id1,myTable.originalID,myTable.name,myTable.place
FROM        (myTable, (SELECT @n:=0) r1)
LEFT JOIN   (SELECT @i:=@i+1 AS id2,originalID,name,place FROM (myTable, (SELECT @i:=0) r2) WHERE originalID!=12) secondTable
ON          id1=id2;

我能做什么？

Answer 1

它们是未知的，因为查询中唯一已知的列(作为一般规则)是 from 子句中的列。您在 select 子句中定义它们。尝试将变量放入子查询中，例如:

select *
from (select @n := @n + 1 AS id1, mt.originalID, mt.name, mt.place
      from myTable mt cross join
           (select @n := 0) const
    ) t1 left join
    (SELECT @i := @i + 1 AS id2, originalID, name, place
     FROM myTable cross join
          (SELECT @i:=0) r2
     WHERE originalID <> 12
    ) secondTable
    ON t1.id1 = secondtable.id2;