在 MariaDB/MySQL 中，如何从单行返回的不同记录中检索同一列？

Question

我想检索一行，显示属于特定集合的产品的前三种颜色。 顺序是预定义的，对于某些上下文，我检索顶部颜色的方式如下。 但是我需要在三个不同的字段中但在一行中显示前三种颜色。

SELECT
   color
FROM
   product
WHERE
   category_id = 100
ORDER BY
   FIELD(p.color, 'Red','Orange','Blue','Yellow','Pink','Purple','Brown','Green','Clear','unknown','')
LIMIT 1

我想要最后“LIMIT 3”的效果，但我需要一行，而不是三行。

Answer 1

检索 3 行并将结果与GROUP_CONCAT合并。

SELECT GROUP_CONCAT(color)
FROM (
    SELECT
       DISTINCT color
    FROM
       product
    WHERE
       category_id = 100
    ORDER BY
       FIELD(p.color, 'Red','Orange','Blue','Yellow','Pink','Purple','Brown','Green','Clear','unknown','')
    LIMIT 3
) x

如果您需要它们在结果中的单独列中，您可以将子查询放在SELECT列表中，并使用不同的LIMIT子句。

SELECT (
    SELECT
       DISTINCT color
    FROM
       product
    WHERE
       category_id = 100
    ORDER BY
       FIELD(p.color, 'Red','Orange','Blue','Yellow','Pink','Purple','Brown','Green','Clear','unknown','')
    LIMIT 0, 1) AS first,
    SELECT
       DISTINCT color
    FROM
       product
    WHERE
       category_id = 100
    ORDER BY
       FIELD(p.color, 'Red','Orange','Blue','Yellow','Pink','Purple','Brown','Green','Clear','unknown','')
    LIMIT 1, 1) AS second,
    SELECT
       DISTINCT color
    FROM
       product
    WHERE
       category_id = 100
    ORDER BY
       FIELD(p.color, 'Red','Orange','Blue','Yellow','Pink','Purple','Brown','Green','Clear','unknown','')
    LIMIT 2, 1) AS third

Answer 2

这是你想要的吗？

SELECT GROUP_CONCAT(color ORDER BY cnt DESC) as colors
FROM (SELECT p.color, COUNT(*) as cnt
      FROM product p
      WHERE p.category_id = 100 AND
            p.color IN ('Red', 'Orange', 'Blue', 'Yellow',' Pink', 'Purple', 'Brown', 'Green', 'Clear', 'unknown', '')
      GROUP BY p.color
      ORDER BY COUNT(*) DESC
      LIMIT 3
     ) p;

如果颜色出现一次并且TOP指的是排序，则使用GROUP_CONCAT(ORDER BY :

SELECT GROUP_CONCAT(color ORDER BY FIELD(p.color, 'Red', 'Orange', 'Blue', 'Yellow', 'Pink', 'Purple', 'Brown', 'Green', 'Clear', 'unknown', '')) as colors
FROM product
WHERE category_id = 100;