为什么我得到子查询错误

Question

我的脚本在这里。这是我的查询，我使用paint来显示我的错误：

我想要的输出是从计划表中选择工作日名称='星期六'左连接到时间表所以

示例今天的日期是7/29/2017然后=星期六

SELECT effectiveDate,

CASE

  WHEN (SELECT DATE_FORMAT(effectiveDate, '%W') = 'Saturday'

  FROM schedules LEFT JOIN timesheet ON schedules.empid = timesheet.empid
  AND timesheet.date = schedules.effectiveDate  GROUP BY effectiveDate)

  THEN 'Saturday'

END

FROM schedules
LEFT JOIN timesheet ON schedules.empid = timesheet.empid AND timesheet.date = schedules.effectiveDate


WHERE effectiveDate <= CURDATE()
AND YEAR(effectiveDate) = YEAR(CURDATE())
AND MONTH(effectiveDate) = MONTH(CURDATE()) AND schedules.empid = '40'
GROUP BY effectiveDate

Answer 1

您不需要子查询（与主查询相同），只需直接引用该列。

此外，您可以使用DAYNAME功能获取当天的名称，而不是DATE_FORMAT。

SELECT effectiveDate,
       CASE
            WHEN DAYNAME(effectiveDate) = 'Saturday'
            THEN 'Saturday'
       END AS day
FROM schedules
LEFT JOIN timesheet ON schedules.empid = timesheet.empid AND timesheet.date = schedules.effectiveDate
WHERE effectiveDate <= CURDATE()
AND YEAR(effectiveDate) = YEAR(CURDATE())
AND MONTH(effectiveDate) = MONTH(CURDATE()) AND schedules.empid = '40'
GROUP BY effectiveDate

Answer 2

您不需要子查询。您可以在选择查询中直接访问effectiveDate并执行相同的操作。

SELECT effectiveDate,
CASE
  WHEN DATE_FORMAT(effectiveDate, '%W')  = 'Saturday'
  THEN 'Saturday'
  ELSE 'Something else'
END AS day
FROM schedules
LEFT JOIN timesheet ON schedules.empid = timesheet.empid AND timesheet.date = schedules.effectiveDate
WHERE effectiveDate <= CURDATE()
AND YEAR(effectiveDate) = YEAR(CURDATE())
AND MONTH(effectiveDate) = MONTH(CURDATE()) AND schedules.empid = '40'
GROUP BY effectiveDate