Summary: in this tutorial, you will learn various ways to delete duplicate rows in MySQL.

How To Delete Duplicates In Oracle
How To Remove Duplicates In Oracle From Select
How To Eliminate Duplicates In Oracle
How To Delete Duplicates In Oracle Sql
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Use RANK to delete duplicate rows This is an example of the RANK function to identify and remove duplicate rows from Oracle tables, which deletes all duplicate rows while leaving the initial instance of the duplicate row. Been using the following regexpreplace to create a comma separated string for those values in ' colname ' and remove any duplicates. REGEXPREPLACE (RTRIM (XMLAGG (XMLELEMENT (E,colname,',').EXTRACT ('//text ')).GetClobVal ,','),' (^,+) (, 1)+', ' 1') Works ok but with 1 exception - if 'colname' has empty string values. In Oracle there are many ways to delete duplicate records. Note that below example are described to just explain the different possibilities.

In the previous tutorial, we have shown you how to find duplicate values in a table. Once the duplicates rows are identified, you may want to delete them to clean up your data.

How To Delete Duplicates In Oracle

Prepare sample data

The following script creates tablecontacts and inserts sample data into the contacts table for the demonstration.

Note that you can execute this script to recreate test data after you execute a DELETE statement.

This query returns data from the contacts table:

The following query returns the duplicate emails in the contacts table:

As you can see, we have four rows with duplicate emails.

A) Delete duplicate rows using `DELETE JOIN` statement

MySQL provides you with the DELETE JOIN statement that allows you to remove duplicate rows quickly.

The following statement deletes duplicate rows and keeps the highest id:

This query references the contacts table twice, therefore, it uses the table alias t1 and t2.

The output is:

It indicated that four rows have been deleted. You can execute the query that find duplicate emails again to verify the delete:

The query returns an empty set, which means that the duplicate rows have been deleted.

How To Remove Duplicates In Oracle From Select

Let’s verify data from the contacts table:

The rows with id 2, 4, 7, and 9 have been deleted.

In case you want to delete duplicate rows and keep the lowest id, you can use the following statement:

Note that you can execute the script for creating contacts table again and test this query. The following output shows the data of the contacts table after removing duplicate rows.

B) Delete duplicate rows using an intermediate table

How To Eliminate Duplicates In Oracle

The following shows the steps for removing duplicate rows using an intermediate table:

Create a new table with the structure the same as the original table that you want to delete duplicate rows.
Insert distinct rows from the original table to the immediate table.
Drop the original table and rename the immediate table to the original table.

The following queries illustrate the steps:

Step 1. Create a new table whose structure is the same as the original table:

Step 2. Insert distinct rows from the original table to the new table:

Step 3. drop the original table and rename the immediate table to the original one

How To Delete Duplicates In Oracle Sql

For example, the following statements delete rows with duplicate emails from the contacts table:

C) Delete duplicate rows using the `ROW_NUMBER()` function

Note that the ROW_NUMBER() function has been supported since MySQL version 8.02 so you should check your MySQL version before using the function.

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The following statement uses the ROW_NUMBER() function to assign a sequential integer number to each row. If the email is duplicate, the row number will be greater than one.

The following statement returns id list of the duplicate rows:

And you just delete the duplicate rows from the contacts table using the DELETE statement with a subqueryin the WHERE clause:

MySQL issued the following message:

In this tutorial, you have learned how to delete duplicate rows in MySQL by using the the DELETE JOIN statement or an intermediate table.