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SQL Puzzle | Create 0 – 1 Flag ( 0 – Last ROW) | THE SINGLE SELECT Interview Question

In this puzzle you have to generate a new column called Flagger The criteria is for each Vals last row the flagger should be 0 all else is 1.

Please check the sample input and the expected output.

Sample Input

Id Vals
101 SQL
102 SQL
103 Oracle
104 Oracle
105 Oracle
106 DB2
107 DB2
108 mySQL
109 mySQL
110 mySQL
111 mySQL

Expected Output

Id Vals Flagger
101 SQL 1
102 SQL 0
103 Oracle 1
104 Oracle 1
105 Oracle 0
106 DB2 1
107 DB2 0
108 mySQL 1
109 mySQL 1
110 mySQL 1
111 mySQL 0

Use below script to create table and insert sample data into it.

--

CREATE TABLE CreateFlagger
(
	 Id INT
	,Vals VARCHAR(10)
)
GO

INSERT INTO CreateFlagger VALUES
(101,'SQL'),
(102,'SQL'),
(103,'Oracle'),
(104,'Oracle'),
(105,'Oracle'),
(106,'DB2'),
(107,'DB2'),
(108,'mySQL'),
(109,'mySQL'),
(110,'mySQL'),
(111,'mySQL')
GO

SELECT * FROM CreateFlagger
GO

--

Rules/Restrictions

The solution should be should use “SELECT” statement or “CTE”.

Add your solution(s) in the comments section or send you solution(s) to pawankkmr@gmail.com

SOLUTION – 1 | USING FIRST_VALUE Method..

--


SELECT * , CASE WHEN FIRST_VALUE(Id) OVER (PARTITION BY Vals ORDER BY Id DESC) = Id THEN 0 ELSE 1 END Flagger
FROM CreateFlagger
ORDER BY Id


--

Output-1

--                            


Id          Vals       Flagger
----------- ---------- -----------
101         SQL        1
102         SQL        0
103         Oracle     1
104         Oracle     1
105         Oracle     0
106         DB2        1
107         DB2        0
108         mySQL      1
109         mySQL      1
110         mySQL      1
111         mySQL      0

(11 rows affected)




--

SOLUTION – 2 | USING ROW_NUMBER() Method.. | Of Course 2 SELECTs

--


SELECT Id,Vals,CASE WHEN rnk = 1 THEN 0 ELSE 1 END Flagger
FROM
(
	SELECT * , ROW_NUMBER() OVER (PARTITION BY Vals ORDER BY Id DESC) rnk
	FROM CreateFlagger
)t ORDER BY Id

--

Output-2

--                            


Id          Vals       Flagger
----------- ---------- -----------
101         SQL        1
102         SQL        0
103         Oracle     1
104         Oracle     1
105         Oracle     0
106         DB2        1
107         DB2        0
108         mySQL      1
109         mySQL      1
110         mySQL      1
111         mySQL      0

(11 rows affected)



--

Add a comment if you have any other or better solution in mind. I would love to learn it. We all need to learn.

Pawan Khowal

Pawan is a SQL Server Developer. If you need any help in writing code/puzzle or training please email at – pawankkmr”AT”gmail.com. Meanwhile please go throgh the top pages from his blog.

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