我一直在获取连接表上的SUM时总是遇到麻烦,总是有一个问题,我可以通过运行两个查询来获得所需的结果,我想知道这两个查询是否可以组合在一起以构成一个连接查询,这是我查询的结果有和我尝试加入查询
查询1
SELECT last_name, first_name, DATE_FORMAT( (mil_date), '%m/%d/%y' ) AS dates, SUM( drive_time ) MINUTES FROM bhds_mileage LEFT JOIN bhds_teachers i ON i.ds_id = bhds_mileage.ds_id WHERE mil_date BETWEEN '2016-04-11' AND '2016-04-30' AND bhds_mileage.ds_id =5 GROUP BY CONCAT( YEAR( mil_date ) , '/', WEEK( mil_date ) ) ,
bhds_mileage.ds_id ORDER BY last_name ASC , dates ASC 以分钟为单位的输出是271、281、279
查询2
SELECT last_name, first_name, DATE_FORMAT((tm_date), '%m/%d/%y') AS dates,
SUM(tm_hours) total FROM bhds_timecard LEFT JOIN bhds_teachers i ON i.ds_id = bhds_timecard.ds_id WHERE tm_date BETWEEN '2016-04-11' AND '2016-04-30' AND bhds_timecard.ds_id = 5 GROUP BY CONCAT(YEAR(tm_date), '/', WEEK(tm_date)), bhds_timecard.ds_id ORDER BY last_name ASC, dates ASC 这里的输出是33.00,36.00,26.75
现在我尝试加入查询
SELECT last_name, first_name, DATE_FORMAT((tm_date), '%m/%d/%y') AS dates,
SUM(tm_hours) total, SUM( drive_time ) MINUTES FROM bhds_timecard LEFT JOIN bhds_teachers i ON i.ds_id = bhds_timecard.ds_id LEFT JOIN bhds_mileage ON DATE_FORMAT((bhds_timecard.tm_date), '%m/%d/%y') = DATE_FORMAT((bhds_mileage.mil_date), '%m/%d/%y') AND bhds_timecard.ds_id = bhds_mileage.ds_id WHERE tm_date BETWEEN '2016-04-11' AND '2016-04-30' AND bhds_timecard.ds_id = 5 GROUP BY CONCAT(YEAR(tm_date), '/', WEEK(tm_date)), bhds_timecard.ds_id 括号是预期的
这输出1044(271),1086(281),1215(279)
在主查询中使用多个联接时,最终会得到所有表的叉积,因此总和将乘以另一个表中匹配的行数。您需要将总和移到子查询中。
SELECT last_name, first_name, DATE_FORMAT(LEAST(mil_date, tm_date), '%m/%d/%y' ) AS dates, total, minutes FROM bhds_teachers AS i LEFT JOIN ( SELECT ds_id, YEARWEEK(mil_date) AS week, MIN(mil_date) AS mil_date, SUM(drive_time) AS minutes FROM bhds_mileage WHERE mil_date BETWEEN '2016-04-11' AND '2016-04-30' AND bhds_mileage.ds_id = 5 GROUP BY ds_id, week) AS m ON m.ds_id = i.ds_id LEFT JOIN ( SELECT ds_id, YEARWEEK(tm_date) AS week, MIN(tm_date) AS tm_date, SUM(tm_hours) AS total WHERE tm_date BETWEEN '2016-04-11' AND '2016-04-30' AND bhds_timecard.ds_id = 5 GROUP BY ds_id, week) AS t ON t.ds_id = i.ds_id AND t.week = m.week来源:stack overflow
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