Strategies For Removal Of Duplicate Records In SQL Server


Data management is one of the key requisites of an organization, irrespective of considering its scale of operations. With the growing competitiveness, it has become important for businesses to maintain a strategic content and thus, keeping confidentiality of information is required. Owing to this fact, numerous software applications have come to the picture, which features a set of individual attributes aimed to facilitate a proper data management and recovery framework.

Brief on SQL Server

SQL server is one such (RDBMS) Relational Database Management System launched by Microsoft, which has been designed for working in the enterprise environment. It functions on (Transact- SQL) T-SQL, which is a set of various programming extensions from Microsoft and Sybase for adding several features to the standard one, including transaction control, error handling and exception, declared variables and row processing.

In spite of having a set of valuable attributes, which helps organizations to facilitate accurate database management, often administrators encounter with certain problems related to deleting duplicate records from this RDBMS. Following here are certain effective strategies, which will help to do the same seamlessly.

Problem: Mostly in the process of extraction, transformation and loading in various data warehousing applications, they are being encountered with a set of duplicate records piled up in the table. For making the table data precise and consistent, the administrators need to eliminate these records.

Solution: Addressing this issue, here are three different strategies to for de-duplication records.

Usage of Correlated Sub-Queries

In case, there is already an identity column present on the table, get assured that the task is half done. One can certainly use a correlated sub-query for getting rid of such duplicates. Mostly, in the correlated sub-query, the first outer query is evaluated. The outcome of outer query is utilized by an inner sub-query to further evaluate, irrespective of whatever is the result of inner sub-query achieved by outer query for getting the ultimate result.

Usage of Temporary Tables

In this specific approach, administrators pull the distinct records present in the target table to one temporary table. Thereafter, they need to shorten the target table, thereby finally place the records from temporary tables again back to target table. While undergoing the task, people need to sure of having enough space for tempdb database to retain all distinct records.

Usage of CTE

SQL Server 2005 launched the CTE, Common Table Expression; that acts as set of temporary results defined within execution of one single Insert, Select, Delete, Update or Create View instructions.

Usage of Unclear Group Transformation Held in SSIS

If someone is willing to use SSIS for uploading the data to target table, he can utilize the Fuzzy Group Transformation prior to inserting the records to destination table for ignoring duplicate records, thereby placing unique records only.

These four strategies will certainly help in removing duplicate records, which are generated in the process of data transfer in SQL server. Moreover, if someone is having the need to export data from SQL server, it is crucial for him to keep note of these kinds of problems, which will ensure the task to be performed seamlessly.