如何獲得此SQL查詢以輸出兩行而不是兩個字段？

Question

這是我的SQL查詢，它產生一個單獨的結果行，有兩列「下」和「更高」。這些對應於Rankable表中行的主鍵（「id」）。

該查詢的目的是選擇一個隨機的一對Rankable行，它不在比較表中（它包含所有先前的對）。

但是，我需要的是這個查詢將兩個Rankable作爲行返回，而不僅僅是單行中的可排序ID作爲字段。

這是當前查詢：

SELECT a.id AS lower, b.id AS higher 
FROM Rankable a 
INNER JOIN Rankable b on a.id < b.id 
WHERE 
    a.category_id = ? AND b.category_id = ? 
    AND NOT EXISTS (
    SELECT * 
    FROM Comparison c 
    WHERE c.lower_id in (a.id, b.id)) 
    AND NOT EXISTS (
    SELECT * 
    FROM Comparison c 
    WHERE c.higher_id IN (a.id, b.id)) 
ORDER BY a.id * rand() 
LIMIT 1; 

Answer 1

我稱之爲MySQL的黑客..

select @a as one 
from 
(

    SELECT @a := a.id, @b := b.id 
    FROM Rankable a 
    INNER JOIN Rankable b on a.id < b.id 
    WHERE 
     a.category_id = ? AND b.category_id = ? 
     AND NOT EXISTS (
     SELECT * 
     FROM Comparison c 
     WHERE c.lower_id in (a.id, b.id)) 
     AND NOT EXISTS (
     SELECT * 
     FROM Comparison c 
     WHERE c.higher_id IN (a.id, b.id)) 
    ORDER BY a.id * rand() 
    LIMIT 1 
) SQ 
union all 
select @b 

要加入到表來獲取所有其他列：

select Rankable.* 
from 
(
    select 1 as Sort, @a as one 
    from 
    (

     SELECT @a := a.id, @b := b.id 
     FROM Rankable a 
     INNER JOIN Rankable b on a.id < b.id 
     WHERE 
      a.category_id = ? AND b.category_id = ? 
      AND NOT EXISTS (
      SELECT * 
      FROM Comparison c 
      WHERE c.lower_id in (a.id, b.id)) 
      AND NOT EXISTS (
      SELECT * 
      FROM Comparison c 
      WHERE c.higher_id IN (a.id, b.id)) 
     ORDER BY a.id * rand() 
     LIMIT 1 
    ) SQ 
    union all 
    select 2, @b 
) X 
INNER JOIN Rankable ON Rankable.Id = X.one 
ORDER BY X.Sort 

Answer 2

創建2個查詢一個較低和一個較高的級別，然後聯合在一起。 用等級創建一個靜態列來標識哪個是哪個。 「高」或「秩

Answer 3

不漂亮較低，但我認爲這將工作：

SELECT * FROM Rankable JOIN (
    SELECT a.id AS lower, b.id AS higher 
    FROM Rankable a 
    INNER JOIN Rankable b on a.id < b.id 
    WHERE  
    a.category_id = ? AND b.category_id = ? 
    AND NOT EXISTS (
     SELECT * 
     FROM Comparison c 
     WHERE c.lower_id in (a.id, b.id) 
    ) 
    AND NOT EXISTS (
     SELECT * 
     FROM Comparison c 
     WHERE c.higher_id IN (a.id, b.id) 
    ) 
    ORDER BY a.id * rand() 
    ) AS rank_them 
ON (Rankable.id = rank_them.higher OR Rankable.id = rank_them.lower)