Wednesday, March 18, 2009

The SQL SELECT DISTINCT Statement

In a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes you will want to list only the different (distinct) values in a table.

The DISTINCT keyword can be used to return only distinct (different) values.

SQL SELECT DISTINCT Syntax
SELECT DISTINCT column_name(s) FROM table_name



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SELECT DISTINCT Example
The "Persons" table:



Now we want to select only the distinct values from the column named "City" from the table above.

We use the following SELECT statement:

DECLARE @Persons TABLE (LogRef int, FirstName varchar(30),LastName varchar(30),Address varchar(50),City varchar(50))
INSERT INTO @Persons
SELECT 1, 'Serkan','SONMEZ','Altiparmak Mh','Bursa'
UNION SELECT 2, 'Egemen','TANIRER','Muradiye Mh.','Trabzon'
UNION SELECT 3, 'Ozkan','YAKUT','Ataevler Mh.','Ankara'
UNION SELECT 4, 'Rahmi','TABAN','Kadıkoy','Istanbul'
UNION SELECT 4, 'Didem','KIZILKAYA','Sarıyer','Istanbul'

SELECT DISTINCT City FROM @Persons


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