Delete duplicate rows from the table using row_number()

If Exists(Select * From tempdb.Information_Schema.Tables Where Table_Name Like '#Temp%')
    Drop Table #temp

Create Table #temp ([Id] int, [Name] varchar(50), [Age] int, [Sex] bit default 1)
Go

Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(1,'James',25,default)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(1,'James',25,default)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(1,'James',25,default)

Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(2,'Lisa',24,0)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(2,'Lisa',24,0)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(2,'Lisa',24,0)

Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(3,'Mirsa',23,0)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(3,'Mirsa',23,0)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(3,'Mirsa',23,0)

Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(4,'John',26,default)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(5,'Abraham',28,default)
Insert Into #temp ([Id] , [Name] , [Age] , [Sex] ) Values(6,'Lincoln',30,default)


Delete T From
(Select Row_Number() Over(Partition By [ID],[Name],[Age],[Sex] order By [ID]) As RowNumber,* From #Temp)T
Where T.RowNumber > 1


Select * From #temp

SQL SERVER – Difference Between Unique Index vs Unique Constraint

Unique Index and Unique Constraint are the same. They achieve same goal. SQL Performance is same for both.

Add Unique Constraint
ALTER TABLE dbo. ADD CONSTRAINT
UNIQUE NONCLUSTERED
(

) ON [PRIMARY]

Add Unique Index
CREATE UNIQUE NONCLUSTERED INDEX
ON dbo.
(

) ON [PRIMARY]

There is no difference between Unique Index and Unique Constraint. Even though syntax are different the effect is the same. Unique Constraint creates Unique Index to maintain the constraint to prevent duplicate keys. Unique Index or Primary Key Index are physical structure that maintain uniqueness over some combination of columns across all rows of a table. It is a convenient way to enforce a Unique Constraint for SQL Server.

Comparison and Difference between HAVING and WHERE Clause

HAVING specifies a search condition for a group or an aggregate function used in SELECT statement.


HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause.

A HAVING clause is like a WHERE clause, but applies only to groups as a whole, whereas the WHERE clause applies to individual rows. A query can contain both a WHERE clause and a HAVING clause. The WHERE clause is applied first to the individual rows in the tables . Only the rows that meet the conditions in the WHERE clause are grouped. The HAVING clause is then applied to the rows in the result set. Only the groups that meet the HAVING conditions appear in the query output. You can apply a HAVING clause only to columns that also appear in the GROUP BY clause or in an aggregate function. (Reference :BOL)

Example of HAVING and WHERE in one query:

SELECT titles.pub_id, AVG(titles.price)
FROM titles INNER JOIN publishers
ON titles.pub_id = publishers.pub_id
WHERE publishers.state = 'CA'
GROUP BY titles.pub_id
HAVING AVG(titles.price) > 10

Sometimes you can specify the same set of rows using either a WHERE clause or a HAVING clause. In such cases, one method is not more or less efficient than the other. The optimizer always automatically analyzes each statement you enter and selects an efficient means of executing it. It is best to use the syntax that most clearly describes the desired result.