How to Remove Duplicates in Sql

What is SQL?

SQL stands for Structured Query Language and becomes first off developed with the aid of IBM inside the 70s to engage with relational databases. It is the not unusual language for databases, remains quite readable and its miles especially easy to take a look at the basics (although the language may be very effective).             

How to Find and Delete Duplicates in SQL

According to database design first-class practices, a SQL Server table should not include reproduction rows. During the database layout technique, primary keys must be created to take away replica rows. However, once in a while we need to paintings with databases where these rules are not observed or exceptions are possible (whilst these rules are bypassed knowingly).

DISTINCT is useful in certain instances, but it has the drawback that it may growth load at the query engine to carry out the kind (since it needs to evaluate the end result set to itself to cast off duplicates).

Find and Remove Duplicates Using Row in SQL

A simple query for finding and removing the duplicates from the table using row numbers.

WITH CTE ( Col1 , Col2 , Col3 , DuplicateCount ) AS ( SELECT Col1, Col2, Col3, ROW_NUMBER( )

OVER ( PARTITION BY Col1 , Col2 , Col3

ORDER BY Col1 )

AS DuplicateCount

FROM MyTable )

SELECT * from CTE Where DuplicateCount = 1

Find and Remove Duplicates Using Self Join in SQL

A simple table schema is given below:

( emp_name    emp_address   sex         matial_status )

A Query:

SELECT emp_name , emp_address , relationship , marital_status

from MyTable a

WHERE NOT EXISTS (

select 1

from MyTable b

where   b.emp_name = a.emp_name AND

b.emp_address = a.emp_address AND
b.sex = a.sex AND
b.create_date > = a.create_date

);

Find and Removing using Group By in SQL

We can also find and remove duplicates data from a table using Group By clause in SQL. A simple example is given below:

SELECT FirstName , LastName , MobileNo , COUNT ( * ) AS CNT
FROM CUSTOMER
GROUP BY FirstName , LastName , MobileNo
HAVING COUNT ( * ) = 1

How to Remove Duplicates in SQL Table

Let’s a simple table is given below:

Create a Table MyTable (

RowID int not null identity(1,1) primary key,

Col1 varchar(20) not null,

Col2 varchar(2048) not null,

Col3 tinyint not null

);

Now we delete duplicates from it.

SELECT RowID,
COUNT ( * ) TotalCount
FROM MyTable
GROUP BY RowID
HAVING COUNT ( * ) > 1
ORDER BY COUNT ( * ) DESC

Above query will delete the duplicates from RowID column.

Find and Remove Duplicates Using Row Value wise in SQL

Now using row wise , another simple example finding and removing duplicates in row wise:

DELETE TableName

WHERE id not in ( SELECT MAX ( id ) FROM TableName GROUP BY Value ) ;

We can improve our results using this query:

DELETE from TableName O

WHERE id < ( SELECT MAX ( columnName ) FROM TableName AS m                          

WHERE m.Value = O.Value GROUP BY Value ) ;

How do I remove duplicates from a query?

How remove duplicates in SQL join?

How do I delete duplicates but keep one?

Can I remove duplicates in Excel?

How do I remove duplicates from a list?

How do I remove duplicates in multiple columns?

How do I remove duplicates in numbers?

How do I remove duplicates from a CSV file?

How do you count duplicates in Excel?

How do I count duplicates in SQL?

How do you use Countifs?

Is Countifs AND or OR?

Why is Countifs not working?

What is difference between Countif and Countifs?