5 Methods to Delete Duplicate Rows for Optimization in SQL
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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