分组不正确 SQL 查询

Question

我需要创建一个 SQL 将使用以下数据的查询：

shift_id, emp_id,   date,    starttime, endtime
   1    ,  55   , 2015-10-14, 06:00:00, 10:00:00
   2    ,  55   , 2015-10-15, 03:00:00, 13:00:00
   3    ,  52   , 2015-10-15, 07:00:00, 14:00:00

然后 re-arrange 它会在顶部显示 'date' 作为一列，开始日期是下一个星期日。我已经开始尝试下面但是如果有2名员工（emp_id）在同一天工作，它不会显示分组：

SELECT concat(firstname,' ', surname) AS 'Fname', 
    (CASE WHEN DAYOFWEEK(date) = 1 THEN concat(starttime,'-', endtime) END) `Sunday`,
    (CASE WHEN DAYOFWEEK(date) = 2 THEN concat(starttime,'-', endtime) END) `Monday`,
    (CASE WHEN DAYOFWEEK(date) = 3 THEN concat(starttime,'-', endtime)  END) `Tuesday`,
    (CASE WHEN DAYOFWEEK(date) = 4 THEN concat(starttime,'-', endtime)  END) `Wednesday`,
    (CASE WHEN DAYOFWEEK(date) = 5 THEN concat(starttime,'-', endtime)  END) `Thursday`,
    (CASE WHEN DAYOFWEEK(date) = 6 THEN concat(starttime,'-', endtime)  END) `Friday`,
    (CASE WHEN DAYOFWEEK(date) = 7 THEN concat(starttime,'-', endtime)  END) `Saturday`
FROM shifts NATURAL JOIN employees
GROUP BY Fname, date

这是两次显示员工姓名而不是分组的结果？我哪里做错了？:

使用GROUP_CONCAT，错误的结果如下：

Answer 1

这是您要找的吗？如果没有，请做一个样本结果。第一个SELECT只是为了隐藏一些tmp字段。如果您通过程序获得结果，您可以将其删除

SELECT Fname, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
FROM (
  SELECT 
      @timestr:=  concat(starttime,'-', endtime) AS a,
      @datenr:= DAYOFWEEK(DATE) AS b,
      concat(firstname,' ', surname) AS 'Fname',
      COALESCE( IF(@datenr  = 1, @timestr,''))  AS `Sunday`,
      COALESCE( IF(@datenr  = 2, @timestr,''))  AS `Monday`,
      COALESCE( IF(@datenr  = 3, @timestr,''))  AS `Tuesday`,
      COALESCE( IF(@datenr  = 4, @timestr,''))  AS `Wednesday`,
      COALESCE( IF(@datenr  = 5, @timestr,''))  AS `Thursday`,
      COALESCE( IF(@datenr  = 6, @timestr,''))  AS `Friday`,
      COALESCE( IF(@datenr  = 7, @timestr,''))  AS `Saturday`
  FROM shifts s
  LEFT JOIN employees e ON e.emp_id = s.emp_id
  GROUP BY s.date, s.emp_id
) AS result;

Answer 2

您选择的列多于您在 GROUP BY 中指定的列。结果，MySQL 将简单地从该组中的一条记录中选取数据来表示它：https://dev.mysql.com/doc/refman/5.5/en/group-by-handling.html

MySQL extends the use of GROUP BY so that the select list can refer to nonaggregated columns not named in the GROUP BY clause. This means that the preceding query is legal in MySQL. You can use this feature to get better performance by avoiding unnecessary column sorting and grouping. However, this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate.

尝试这样的事情：

SELECT concat(firstname,' ', surname) AS 'Fname', 
    MAX(CASE WHEN DAYOFWEEK(date) = 1 THEN concat(starttime,'-', endtime) END) `Sunday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 2 THEN concat(starttime,'-', endtime) END) `Monday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 3 THEN concat(starttime,'-', endtime)  END) `Tuesday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 4 THEN concat(starttime,'-', endtime)  END) `Wednesday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 5 THEN concat(starttime,'-', endtime)  END) `Thursday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 6 THEN concat(starttime,'-', endtime)  END) `Friday`,
    MAX(CASE WHEN DAYOFWEEK(date) = 7 THEN concat(starttime,'-', endtime)  END) `Saturday`
FROM shifts NATURAL JOIN employees
GROUP BY Fname, date

分组不正确 SQL 查询

Incorrect grouping SQL Query

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