5 Methods to Delete Duplicate Rows for Optimization in SQL

by Tosska Technologies sql server performance tuning- Tosska Technologies

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Database professionals have always talked about the importance of following certain techniques to ensure optimization in SQL. Some examples include the necessity of constraints (such as primary keys) and other elements in a table for data integrity and optimal performance.

However, users sometimes encounter problems despite taking all the precautions and following the best practices. For instance, duplicate rows tend to come from nowhere and even show up in intermediate tables when a user imports data.

These affect database speed and therefore, must be eliminated before the user inserts them into the production tables. In this article, we will discuss the best ways to get rid of duplicate rows from tables to improve performance of SQL query in your database.

Using the SQL RANK function: This function provides unique row identification numbers for every row regardless of the redundant rows. You can add a ‘partition by’ clause to it in order to help you remove the rows that are repeating. That’s because the ‘partition by’ clause creates a data subset for the columns you specify and assigns a rank for that partition.
Using HAVING and GROUP BY: The GROUP BY clause in SQL helps locate the redundant rows. It does this by creating groups of data on the basis of the columns the database defines. After this, you can apply the COUNT function to investigate the number of times the row repeats in the database.
Using CTE (Common Table Expressions): You can get rid of any number of duplicate rows with the help of CTE or Common Table Expressions in SQL Server. Introduced in SQL Server 2005, it involves the use of the ROW NUMBER function and assigns a unique sequential number to every row.

One way to tackle this situation with the help of CTE can include the following steps:

● Partitioning the data with the help of the PARTITION BY clause for at least three columns

● Generating a row sequence for every row

● Delete the row numbers that repeat

Using SSIS (SQL Server Integration Service) package: This service package offers a host of transformational operators that are of use to many developers and database professionals. These helps decrease manual effort while increasing optimize oracle query. This package is also capable of eliminating repetitive rows from a SQL table.
Using the SORT operator: All you have to do for this method is create the SSIS package and use the SORT operator from it to sort the values in the table and delete the ones that repeat. Here are the steps explained in brief -

● Go to SQL Server Data Tools and initiate a new integration package.

● Add an OLE database source link in this new package. This proves useful for users who want to improve performance of SQL query.

● Switch to the source editor for the OLE database, adjust the source connection, and pick the destination table.

● Select the Preview option for a look at all the duplicate information inside the source table.

● Include the Sort operator from the SQL Server Integration Service toolbox and link it to the source data so you can delete the duplicate rows.

● If you want to make changes to the data manipulated by the SORT operator, double click on the tool and pick the columns holding the repeating values. You may also apply the ascending or descending sorting functions for the columns.

Most users use the ascending technique that allows them to select the order in which the database sorts the columns. You can spot the duplicate sort values that need to be removed at the bottom on the left to enable optimization in SQL.

Ultimately, each of these methods is effective in deleting duplicate rows from the database for the user. You may prefer one over the other depending on tool availability.

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