There are other ways to remove duplicates which is not discussed in this tip.įor example, we can store distinct rows in a temporary table, then delete all dataįrom our table and after that insert distinct rows from temporary table to our permanent Is an undocumented feature of SQL Server and, therefore, developers should be very While using this approach, it is very important to realize that this Hence, we can conclude that in general, using %%physloc%% does not improve the SELECT ROW_NUMBER() OVER (partition by Value ORDER BY Value) AS RowID, ValueĪnalyzing the Execution Plans, we can see that the first and the last queriesĪre the fastest when compared to the overall batch times: (SELECT %%physloc%% as RowID, value FROM TableB) o Is not used just for comparing performance of all of these options: To the case of the table with a unique index, and in the last query, %%physloc%% In Oracle, the next two are queries for removing duplicates using %%physloc%% similar The first two queries below are the equivalent versions of removing duplicates Thus, we can removeĭuplicate rows from a table without a unique index in SQL Server like in OracleĪs well as like in the case when the table has a unique index. Removing duplicate rows from a table without a unique index. Value of %%physloc%% is unique for each row, we can use it as a row identifier while Is a virtual binary(8) column which shows the physical location of the row. It is called %%physloc%% (since SQL Server 2008) and it Official documentation about this feature, it can be used as an analog to ROWID Despite the fact that it is practically impossible to find Having said that, it is possible to identify the physical address of the row SELECT ROW_NUMBER() OVER (PARTITION BY Value ORDER BY Value) AS RowID, Value WHERE ID IN ( SELECT a.ID FROM TableA a, (SELECT ID, (SELECT MAX(Value) FROM TableA i WHERE o.Value=i.Value GROUP BY Value HAVING o.ID=MAX(i.ID)) AS MaxValue FROM TableA o) bĭeleting the data and looking into the execution plans again we see that theįastest is the first DELETE statement and the slowest is the last as expected: (SELECT ID, RANK() OVER(PARTITION BY Value ORDER BY ID DESC) AS rnk FROM TableA ) bĪs we can see the result for all cases is the same as shown in the screenshot Finding duplicate values in a table with a unique indexįROM TableA a, (SELECT ID, (SELECT MAX(Value) FROM TableA i WHERE o.Value=i.Value GROUP BY Value HAVING o.ID 1
To accomplish our tasks, we need a test environment which we create with the Removing duplicates rows from a SQL Server table with a unique index Test Environment Setup
#Different ways to delete duplicate rows in sql server how to#
In this scenario, the ROW_NUMBER() function canīe used with a common table expression (CTE) to sort the data then delete theĬheck out the examples below to get real world examples on how to delete duplicate
Table with Unique Index - For tables with a unique index, you have the opportunity.In SQL Server there are a number of ways toĪddress duplicate records in a table based on the specific circumstances such as: Withĭuplicate data it is possible for orders to be processed numerous times, have inaccurate How to remove duplicate rows in a SQL Server tableĭuplicate records in a SQL Server table can be a very serious issue. Indexes and contains duplicate rows which should be removed. The second case is that table does not have a primary key or any unique.The first case is when a SQL Server table has a primary key (or unique index)Īnd one of the columns contains duplicate values which should be removed.
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