Using Common Table Expressions in SSIS Scripts

By Tom Nonmacher

Common Table Expressions (CTEs) are a powerful tool in SQL that can simplify complex queries by breaking them down into more manageable pieces. In SQL Server Integration Services (SSIS) scripts, they can be used to improve readability and maintainability. In this post, we will demonstrate how to use CTEs in SSIS scripts across various platforms including SQL Server 2019, MySQL 8.0, DB2 11.5, Azure SQL and Azure Synapse.

A CTE can be thought of as a temporary result set that is defined within the execution scope of a single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement. Once these statements are used, they can refer to the CTE as many times as required. This is particularly useful when the query involves several levels of sub-querying, which can lead to messy and hard-to-read code.

Consider an example in SQL Server 2019. Suppose we have a Sales table and we want to find the total sales for each representative, along with their ranking in terms of sales. The following script uses a CTE to accomplish this: 

WITH Sales_CTE (SalesRep, TotalSales)
AS
(
SELECT SalesRep, SUM(SalesAmount)
FROM Sales
GROUP BY SalesRep
)
SELECT SalesRep, TotalSales, 
RANK() OVER(ORDER BY TotalSales DESC) as SalesRank
FROM Sales_CTE;

The same can be achieved in MySQL 8.0 as follows: 

WITH Sales_CTE AS 
(
SELECT SalesRep, SUM(SalesAmount) as TotalSales
FROM Sales
GROUP BY SalesRep
)
SELECT SalesRep, TotalSales, 
RANK() OVER(ORDER BY TotalSales DESC) as SalesRank
FROM Sales_CTE;

In DB2 11.5, the syntax is slightly different, but the concept remains the same: 

WITH Sales_CTE (SalesRep, TotalSales) AS 
(
SELECT SalesRep, SUM(SalesAmount)
FROM Sales
GROUP BY SalesRep
)
SELECT SalesRep, TotalSales, 
RANK() OVER(ORDER BY TotalSales DESC) as SalesRank
FROM Sales_CTE;

In Azure SQL and Azure Synapse, CTEs work exactly the same as in SQL Server, as they are built on the same database engine. They can be leveraged in SSIS scripts to simplify the code and improve readability, making your ETL processes more efficient and maintainable.

In conclusion, CTEs are an invaluable tool for simplifying complex SQL queries in SSIS scripts. Their temporary nature and scope of execution make them ideal for breaking down complicated queries into more manageable pieces, improving the readability and maintainability of your code. By understanding how to use CTEs in different platforms such as SQL Server 2019, MySQL 8.0, DB2 11.5, Azure SQL and Azure Synapse, you can write more efficient and cleaner SSIS scripts.

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