Understanding PIVOT, and UNPIVOT Statements

Most people seem to find it hard in understanding PIVOT, UNPIVOT, and Reverse PIVOT statements.  This is understandable especially when doing it for the very first time. Just in case you do not know, the PIVOT statement is used to convert table rows into columns whereas the UNPIVOT SQL operator columns back to rows.  Reverse PIVOT statement, on the other hand, refers to the process of applying the UNPIVOT operator to the PIVOTED dataset. This action is aimed at making sure you retrieve the original dataset.

When you want to carry out a simple conversion of columns into rows in SQL Server, it is highly advisable that you make use of UNPIVOT or VALUES structures. As soon as you’re done with the conversion, the received data needs to be used for aggregation or sorting. When this is the case, you need to make use of the VALUES structure as it mostly results in more efficient execution plans.

As for the tables where dissimilar structure types might occur, and there is a restriction in the number of columns, it would be better to use XML. Unlike the dynamic SQL, XML is used inside the table functions.  To be on the safe side, you need to be fully aware of the step-by-step analysis of the execution with the help of SQL Profiler.

One thing you ought to keep in mind is that PIVOT and UPIVOT allow data transformation useful in data modeling, data presentation, and data analysis.  What is even more fascinating is the fact you can implement them easily inside a query processor. This is quite similar to select, project, and join. When having such a design, you’ll get the perfect opportunity for better performance, both during query execution and query optimization.

The Bottom Line

Understanding PIVOT and UNPIVOT statements should never be the underlying reason why you’re going through a hard time. Be sure to carry out a detailed research and examine what they’re all about. Through this action, it is never going to take long before you finally get the most from PIVOT and UNPIVOT statements.

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