间断与孤岛应用：求连续签到天数

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原贴：  https://bbs.csdn.net/topics/392489035?page=1#post-403595581

USE tempdb
GO
IF OBJECT_ID('t') IS NOT NULL DROP TABLE t
GO
CREATE TABLE t(
	id INT IDENTITY(1,1) PRIMARY KEY,
	[name] NVARCHAR(10) NOT NULL DEFAULT('张三'),
	visit_time DATETIME	
)
GO
INSERT INTO t(name,visit_time) VALUES ('张三','2018-12-01 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('张三','2018-12-02 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('张三','2018-12-04 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('张三','2018-12-05 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('张三','2018-12-06 08:00:00')
--
INSERT INTO t(name,visit_time) VALUES ('李四','2018-12-01 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('李四','2018-12-03 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('李四','2018-12-04 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('李四','2018-12-05 08:00:00')
INSERT INTO t(name,visit_time) VALUES ('李四','2018-12-06 08:00:00')

;WITH cte1 AS(
          SELECT *,
                 DATEDIFF(DAY, (SELECT MIN(visit_time) FROM t), visit_time) AS rid
          FROM   t
      ),cte2 AS(
          SELECT NAME,
                 rid,
                 rid -ROW_NUMBER()OVER(PARTITION BY [name] ORDER BY rid) AS diff
          FROM   cte1
      )
      ,cte3 AS (
          SELECT NAME,
                 MIN(rid)  AS start_range,
                 MAX(rid)  AS end_range
          FROM   cte2
          GROUP BY
                 diff,
                 NAME
      )
 
 SELECT 
		cte1.id
		,cte1.[name]
		,cte1.[visit_time]
		,cte1.rid -start_range + 1 AS flag
 FROM   cte3
        INNER JOIN cte1
             ON  cte1.name = cte3.name
             AND cte1.rid BETWEEN cte3.start_range AND cte3.end_range
 ORDER BY
        cte1.name DESC,
        cte1.visit_time