sql - 使用时间跨度对具有相同值的连续行进行分组

Question

抱歉标题含糊(我只是不知道如何描述这个难题)

给出下面的教室时间表:

╔═══════════╦════════════╦═══════════╦═══════════╦═════════╗
║ Classroom ║ CourseName ║  Lesson   ║ StartTime ║ EndTime ║
╠═══════════╬════════════╬═══════════╬═══════════╬═════════╣
║      1001 ║ Course 1   ║ Lesson 1  ║      0800 ║    0900 ║
║      1001 ║ Course 1   ║ Lesson 2  ║      0900 ║    1000 ║
║      1001 ║ Course 1   ║ Lesson 3  ║      1000 ║    1100 ║
║      1001 ║ Course 2   ║ Lesson 10 ║      1100 ║    1200 ║
║      1001 ║ Course 2   ║ Lesson 11 ║      1200 ║    1300 ║
║      1001 ║ Course 1   ║ Lesson 4  ║      1300 ║    1400 ║
║      1001 ║ Course 1   ║ Lesson 5  ║      1400 ║    1500 ║
╚═══════════╩════════════╩═══════════╩═══════════╩═════════╝

我想对表格进行分组以显示:

╔═══════════╦════════════╦═══════════╦═════════╗
║ Classroom ║ CourseName ║ StartTime ║ EndTime ║
╠═══════════╬════════════╬═══════════╬═════════╣
║      1001 ║ Course 1   ║      0800 ║    1100 ║
║      1001 ║ Course 2   ║      1100 ║    1300 ║
║      1001 ║ Course 1   ║      1300 ║    1500 ║
╚═══════════╩════════════╩═══════════╩═════════╝

基本上，我们正在查看一个时间表，显示在特定时间跨度内哪个 crouse 正在使用哪个教室......

我最初的想法是:
按 Classroom 分组和 CourseName并采取Max和 Min对于 start\end时间，但这不会给我显示的时间跨度，好像类(class) 1 正在使用 Classroom 08:00 - 16:00 中间不休息。

Answer 1

如果您使用的是 SQLServer 2012 或更高版本，您可以使用 LAG获取列的前一个值，然后 SUM() OVER (ORDER BY ...)创建一个滚动总和，在这种情况下计算 CourseName 的变化，可用作 GROUP BY anchor

With A AS (
  SELECT ClassRoom
       , CourseName
       , StartTime
       , EndTime
       , PrevCourse = LAG(CourseName, 1, CourseName) OVER (ORDER BY StartTime)
  FROM   Table1
), B AS (
  SELECT ClassRoom
       , CourseName
       , StartTime
       , EndTime
       , Ranker = SUM(CASE WHEN CourseName = PrevCourse THEN 0 ELSE 1 END)
                OVER (ORDER BY StartTime, CourseName)
  FROM   A
)
SELECT ClassRoom
     , CourseName
     , MIN(StartTime) StartTime
     , MAX(EndTime) EndTime
FROM   B
GROUP BY ClassRoom, CourseName, Ranker
ORDER BY StartTime

SQLFiddle demo