How To Filter Out Duplications in the Returning Rows in SQL Server?

If there are duplications in the returning rows, and you want to remove the duplications, you can use the keyword DISTINCT in the SELECT clause. The DISTINCT applies to the combination of all data fields specified in the SELECT clause. The tutorial exercise below shows you how DISTINCT works:

CREATE TABLE fyi_team (first_name VARCHAR(8), 
   last_name VARCHAR(8))
GO

INSERT INTO fyi_team VALUES ('John', 'Gate')
GO
INSERT INTO fyi_team VALUES ('John', 'Russell')
GO
INSERT INTO fyi_team VALUES ('John', 'Seo')
GO
INSERT INTO fyi_team VALUES ('John', 'Gate')
GO
INSERT INTO fyi_team VALUES ('James', 'Gate')
GO
INSERT INTO fyi_team VALUES ('Peter', 'Gate')
GO
INSERT INTO fyi_team VALUES ('John', 'Gate')
GO

SELECT * FROM fyi_team
GO
first_name   last_name
John         Gate
John         Russell
John         Seo
John         Gate
James        Gate
Peter        Gate
John         Gate

SELECT DISTINCT * FROM fyi_team
GO
first_name   last_name
James        Gate
John         Gate
John         Russell
John         Seo
Peter        Gate

SELECT DISTINCT last_name FROM fyi_team
Gate
Russell
Seo

Remember that * in select list represents all columns.

⇒ Group Functions in Query Statements in SQL Server

⇐ Using SELECT Statements on Views in SQL Server

⇑ Using SELECT Statements and GROUP BY Clauses in SQL Server

⇑⇑ SQL Server Database Tutorials