Converting SQL Queries to LINQ with Union

Learn how to effectively convert SQL queries into LINQ queries using the UNION operation, gaining clarity and efficiency in your database interactions.
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Converting SQL Queries to LINQ with Union: A Step-by-Step Guide

When working with databases in C# , developers often encounter the challenge of translating SQL queries into LINQ queries. This can be particularly daunting when dealing with complex SQL features like the UNION operation. In this guide, we will walk through a practical example that demonstrates how to seamlessly convert a SQL query with a UNION into a LINQ query.

The Challenge: Understanding the SQL Query

Let's first take a look at the SQL query we wish to convert. The query performs the following operations:

Selects Document and Item Numbers along with their associated amounts from two different data sources.

Uses a UNION ALL to combine results from the SOP30300 table and the RM20201 table.

Groups the results by Document and Item numbers.

Applies a HAVING clause to filter out groups with a total amount of zero.

Here’s the original SQL query for clarity:

[[See Video to Reveal this Text or Code Snippet]]

The Solution: Crafting the LINQ Query

To convert the provided SQL query into a LINQ query, we can break down the task into manageable parts. The goal is to ensure that our LINQ query mirrors the structure and functionality of the SQL query.

Step 1: Querying the First Data Source

We start by querying the SOP30300 table to fetch the desired document and item details.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Querying the Second Data Source

Next, we execute a query on the RM20201 table and join it with the TRM20201 table. We also need to ensure that we account for nulls in our join.

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Combine and Group the Results

We can then combine the results from both queries using Concat and group them by Document and Item numbers.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Converting SQL queries to LINQ may initially seem challenging, especially with operations like UNION. However, by breaking down the process into clear steps, you can effectively translate complex SQL statements into elegant LINQ queries. This approach not only enhances readability but also maximizes the strengths of C# in data querying.

If you are facing similar challenges with LINQ or have more questions, feel free to drop your queries in the comments below!