SQL Distinct Command

The SQL DISTINCT clause is used together with the SQL SELECT keyword, to return a dataset with unique entries for certain database table column.
 

Example query using Company table for SQL DISTINCT.

FirstName	LastName	Email	DOB	Phone
Scott	Armstrong	Armstrong.yahoo.com	2/4/1968	887-676-2321
Adam	Red	red@himail.com	4/4/1978	792 343-2422
Santo	Harry	Harry@livingin.org	5/24/1978	416 323-3232
Jackson	Jimmy	Jimmy@supermail.co.uk	20/10/1980	416 323-8888

For example if we want to select all distinct surnames from our Company table, we will use the following SQL DISTINCT statement:


SELECT DISTINCT LastName
FROM Company

The result of the SQL DISTINCT expression above will look like this:

LastName

Armstrong

Red

Harry

Jimmy

Because lastname Does not Include any duplicate values all the cells of Lastname wil be included.

The second example i am posting using adventure works database which is sample database from microsoft and can be downloaded from www.codeproject.com for free and can be installed in microsoft sql server 2005/2008.

Select SalesOrderID from Sales.SalesOrderDetail Select distinct SalesOrderID from Sales.SalesOrderDetail

 The first query will return all the SalesOrderID's but second will return distinct SalesOrderID's reducing the number and duplicate values.

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