[英]How do count with inner join and multiple conditions in MySQL
我想查询一次使用每种颜色的次数。
tbl_places是保存来自多个枚举表的数据的主表。 tbl_places为不同建筑物中特定楼层的颜色保留相应的INT值。 `
tbl_paintcolor是具有两列的枚举表:值和颜色。
我不知道如何将ON子句与我想在tbl_places中计数的特定列相关联。
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数同一列。
如何将ON子句中的条件表达式与要在SELECT子句中计数的列相关联?
我希望查询为每个特定楼层输出一列,并且每一行都会计算发现颜色的时间。 该查询的输出结构如下:
╔════════╦════════════╦════════════╦════════════╗
║ Color ║ Blg1Floor1 ║ Blg1Floor2 ║ Blg1Floor3 ║ etc...
╠════════╬════════════╬════════════╬════════════╣
║ red ║ 23 ║ 23 ║ 23 ║
║ orange ║ 23 ║ 23 ║ 23 ║
║ yellow ║ 23 ║ 23 ║ 23 ║
╚════════╩════════════╩════════════╩════════════╝
等等
感谢您的宝贵时间,如果不清楚,我们深表歉意,我是SQL的新手。
我认为您应该尝试将SUM替换为COUNT
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`
使用CASE WHEN
SUM()
可以解决问题。
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`
希望这可以帮助
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