How to display unique comments based on certain conditions in SQL Server?

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SQL-Server-2012

I have to write a query to display unique customer comments from the customer table as shown below:

CUSTOMER TABLE

CustomerID	SequenceNo	Comments
1	1	ABC D
1	2	CDE
1	3	ABC
1	4	ABC D
1	5	CDE
1	6	abc
2	7	ABC DEF
2	8	
2	9	ABC DEF
2	10	DEF
2	11	XYZ 123
2	12	ABC
3	13	PQ RST

Definition of above Customer table will be

SQL

CustomerID	INT
SequenceNo	INT
Comments	VARCHAR(MAX)

I want to write a SQL query to filter the records in the Customer Table and display unique comment history for each customer.

Criterias:
1. Display only Unique Comments from Customer Table for all the customers,
2. If Comments are same then display the row which has maximum SequenceNo
3. Comments can be blank.

Output of the about table would be as shown below:

CustomerID	SequenceNo	Comments
1	3	ABC
1	4	ABC D
1	5	CDE
1	6	abc
2	8	
2	9	ABC DEF
2	10	DEF
2	11	XYZ 123
2	12	ABC
3	13	PQ RST

https://www.dropbox.com/s/h0t3xvvvlaqirk3/11698890_10154036087194466_3495075191431781854_o.jpg?dl=0[^]

Posted 1-Jul-15 11:02am

souravagarwal

Updated 1-Jul-15 11:32am

Maciej Los

v3

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Maciej Los · Answer 1 · 2015-07-01T11:48:00

Have a look at sample:

SQL

DECLARE @tmp TABLE(CustomerID   INT, SequenceNo INT, Comments   VARCHAR(MAX))

INSERT INTO @tmp (CustomerID, SequenceNo, Comments)
VALUES(1, 1, 'ABC D'),
(1, 2, 'CDE'),
(1, 3, 'ABC'),
(1, 4, 'ABC D'),
(1, 5, 'CDE'),
(1, 6, 'abc'),
(2, 7, 'ABC DEF'),
(2, 8, NULL),
(2, 9, 'ABC DEF'),
(2, 10, 'DEF'),
(2, 11, 'XYZ 123'),
(2, 12, 'ABC'),
(3, 13, 'PQ RST')

SELECT CustomerID, SequenceNo, Comments
FROM (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY CustomerID ORDER BY SequenceNo ASC) AS RowNo
    FROM @tmp
    ) AS T
WHERE RowNo > 1

Above query returns:

CustomerID	SequenceNo	Comments
1	2	CDE
1	3	ABC
1	4	ABC D
1	5	CDE
1	6	abc
2	8	NULL
2	9	ABC DEF
2	10	DEF
2	11	XYZ 123
2	12	ABC