SQL - Selecting rows with dates before and after column value change

Question

I have a table called test.
In test I have An ID, a value and a date.
The dates are ordered for each ID.
I want to select rows for an ID, before and after a change of value, so the following example table.

RowNum--------ID------- Value -------- Date
1------------------001 ---------1----------- 01/01/2015
2------------------001 ---------1----------- 02/01/2015
3------------------001 ---------1----------- 04/01/2015
4------------------001 ---------1----------- 05/01/2015
5------------------001 ---------1----------- 06/01/2015
6------------------001 ---------1----------- 08/01/2015
7------------------001 ---------0----------- 09/01/2015
8------------------001 ---------0----------- 10/01/2015
9------------------001 ---------0----------- 11/01/2015
10-----------------001 ---------1----------- 12/01/2015
11-----------------001 ---------1----------- 14/01/2015
12------------------002 ---------1----------- 01/01/2015
13------------------002 ---------1----------- 04/01/2015
14------------------002 ---------0----------- 05/01/2015
15------------------002 ---------0----------- 07/01/2015

The result would return rows 6, 7, 9, 10, 13, 14

Answer 1

You could use analytic functions LAG() and LEAD() to access value in preceding and following rows, then check that it does not match value in current row.

SELECT *
FROM   (
  SELECT RowNum,
         ID,
         Value,
         Date,
         LAG(VALUE, 1, VALUE)  OVER(ORDER BY RowNum)  PrevValue,
         LEAD(VALUE, 1, VALUE) OVER(ORDER BY RowNum)  NextValue
  FROM   test)
WHERE PrevValue <> Value
OR    NextValue <> Value

Params passed to this functions are

1. some scalar expression (column name in this case);
2. offset (1 row before or after);
3. default value ( LAG() will return NULL for first row and LEAD() will return NULL for last row, but they don't seem special in your question, so I used column value as default).

Answer 2

Refer the below one for without using LEAD and LAG:

DECLARE @i        INT = 1, 
        @cnt      INT, 
        @dstvalue INT, 
        @srcvalue INT 

CREATE TABLE #result 
  ( 
     id     INT, 
     mydate DATE 
  ) 

CREATE TABLE #temp1 
  ( 
     rn     INT IDENTITY(1, 1), 
     id     INT, 
     mydate DATE 
  ) 

INSERT INTO #temp1 
            (id, 
             mydate) 
SELECT id, 
       mydate 
FROM   table 
ORDER  BY id, 
          mydate 

SELECT @cnt = Count(*) 
FROM   #temp1 

SELECT @srcvalue = value 
FROM   #temp1 
WHERE  rn = @i 

WHILE ( @i <= @cnt ) 
  BEGIN 
      SELECT @dstvalue = value 
      FROM   #temp1 
      WHERE  rn = @i 

      IF( @srcvalue = @dstvalue ) 
        BEGIN 
            SET @i = @i + 1 

            CONTINUE; 
        END 
      ELSE 
        BEGIN 
            SET @srcvalue = @dstvalue 

            INSERT INTO #result 
                        (id, 
                         mydate) 
            SELECT id, 
                   mydate 
            FROM   #temp 
            WHERE  rn = @i - 1 
            UNION ALL 
            SELECT id, 
                   mydate 
            FROM   #temp 
            WHERE  rn = @i 
        END 

      SET @i = @i + 1 
  END 

SELECT * 
FROM   #result 

Answer 3

The answer using lag() and lead() is the right answer. If you are using a pre-SQL Server 2012 version, then you can do essentially the same thing using cross apply or a correlated subquery:

select t.*
from test t cross apply
     (select top 1 tprev.*
      from test tprev
      where tprev.date < t.date
      order by date desc
     ) tprev cross apply
     (select top 1 tnext.*
      from test tnext
      where tnext.date > t.date
      order by date asc
     ) tnext 
where tprev.value <> tnext.value;