如何使用 MySQL 中的内部连接和多个条件进行计数

Question

我想要一个在每次使用每种颜色时都进行计数的查询。

tbl_places 是主要的 table，它保存来自多个枚举 table 的数据。 tbl_places保存着不同建筑物特定楼层颜色对应的INT值。 `

tbl_paintcolor 是一个包含 2 列的枚举 table：值和颜色。

我不知道如何将 ON 子句与我想在 tbl_places 中计数的特定列联系起来。

SELECT
  `tbl_paintcolor`.`Color` AS Paint_Color,
  count(`tbl_places`.`blg1floor1_color`) AS Blg1Floor1,
  count(`tbl_places`.`blg1floor2_color`) AS Blg1Floor2,
  count(`tbl_places`.`blg1floor3_color`) AS Blg1Floor3
FROM `tbl_places` 
INNER JOIN `tbl_paintcolor` ON (`tbl_places`.`blg1floor1_color`=`tbl_paintcolor`.`Value` OR `tbl_places`.`blg1floor2_color`=`tbl_paintcolor`.`Value`)
GROUP BY `tbl_paintcolor`.`Color`

此查询最终或多或少地计算了同一列。

如何将 ON 子句中的条件表达式与 SELECT 子句中要计数的列相关联？

我希望查询为每个特定楼层输出一列，每行计算找到该颜色的次数。此查询的输出将是结构化的：

╔════════╦════════════╦════════════╦════════════╗
║ Color  ║ Blg1Floor1 ║ Blg1Floor2 ║ Blg1Floor3 ║ etc...
╠════════╬════════════╬════════════╬════════════╣
║ red    ║     23     ║     23     ║     23     ║
║ orange ║     23     ║     23     ║     23     ║
║ yellow ║     23     ║     23     ║     23     ║
╚════════╩════════════╩════════════╩════════════╝

等

感谢您抽出宝贵时间，如果不清楚，我深表歉意，我是 SQL 的新手。

Answer 1

SUM() 和 CASE WHEN 就可以了。

SELECT
      `tbl_paintcolor`.`Color` AS Paint_Color,
      SUM(CASE WHEN `tbl_places`.`blg1floor1_color` IS NOT NULL THEN 1 ELSE 0 END ) AS Blg1Floor1,
      SUM(CASE WHEN `tbl_places`.`blg1floor2_color` IS NOT NULL THEN 1 ELSE 0 END ) AS Blg1Floor2,
      SUM(CASE WHEN `tbl_places`.`blg1floor2_color` IS NOT NULL THEN 1 ELSE 0 END ) AS Blg1Floor3
    FROM `tbl_places` 
    LEFT JOIN `tbl_paintcolor`
    ON (`tbl_places`.`blg1floor1_color`=`tbl_paintcolor`.`Value`
                               OR `tbl_places`.`blg1floor2_color`=`tbl_paintcolor`.`Value`)
    GROUP BY `tbl_paintcolor`.`Color`

希望对您有所帮助

Answer 2

我认为您应该尝试将 COUNT 替换为 SUM

SELECT
    `tbl_paintcolor`.`Color` AS Paint_Color,
    SUM(IF(`tbl_places`.`blg1floor1_color`=`tbl_paintcolor`.`Value`, 1, 0)) AS Blg1Floor1,
    SUM(IF(`tbl_places`.`blg1floor2_color`=`tbl_paintcolor`.`Value`, 1, 0)) AS Blg1Floor2,
    SUM(IF(`tbl_places`.`blg1floor3_color`=`tbl_paintcolor`.`Value`, 1, 0)) AS Blg1Floor3,
FROM `tbl_places` 
INNER JOIN `tbl_paintcolor` ON (
        `tbl_places`.`blg1floor1_color`=`tbl_paintcolor`.`Value` 
        OR `tbl_places`.`blg1floor2_color`=`tbl_paintcolor`.`Value`
        OR `tbl_places`.`blg1floor3_color`=`tbl_paintcolor`.`Value`
)
GROUP BY `tbl_paintcolor`.`Color`

或者您可以尝试的另一种方法是

SELECT `tbl_paintcolor`.`Color` AS Paint_Color,
    (SELECT COUNT(1) AS qty FROM `tbl_places` p1  WHERE p1.`blg1floor1_color`=`tbl_paintcolor`.`Value`) AS Blg1Floor1,
    (SELECT COUNT(1) AS qty FROM `tbl_places` p2  WHERE p2.`blg1floor2_color`=`tbl_paintcolor`.`Value`) AS Blg1Floor2,
    (SELECT COUNT(1) AS qty FROM `tbl_places` p3  WHERE p3.`blg1floor3_color`=`tbl_paintcolor`.`Value`) AS Blg1Floor3
FROM `tbl_paintcolor`

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