Only select first row of repeating value in a column in SQL

Question

I have table that has a column that may have same values in a burst. Like this:

+----+---------+
| id |   Col1  | 
+----+---------+
| 1  | 6050000 |
+----+----         


        

Answer 1

If your RDBMS supports Window Aggregate functions and/or LEAD() and LAG() functions you can leverage them to accomplish what you are trying to report. The following SQL will help get you started down the right path:

SELECT id
     , Col AS CurCol
     , MAX(Col)
       OVER(ORDER BY id ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) AS PrevCol
     , MIN(COL)
       OVER(ORDER BY id ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) AS NextCol
FROM MyTable

From there you can put that SQL in a derived table with some CASE logic that if the NextCol or PrevCol is the same as CurCol then set CurCol = NULL. Then you can collapse eliminate all the id records CurCol IS NULL.

If you don't have the ability to use window aggregates or LEAD/LAG functions your task is a little more complex.

Hope this helps.