How to Get DB2 SQL Result Sets Without Duplicates Using ROW_NUMBER()

Discover how to modify your DB2 SQL queries to eliminate duplicates in your result set by using the `ROW_NUMBER()` function effectively.
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How to Get DB2 SQL Result Sets Without Duplicates Using ROW_NUMBER()

When working with databases, one common challenge developers face is removing duplicate entries from SQL query results. If you're querying a DB2 database and need to filter out duplicates based on specific criteria—like including only a single instance of a value when it has a dash number or is empty—you may find the task quite daunting. In this guide, we will explore a solution to achieve exactly that by utilizing the ROW_NUMBER() function.

Understanding the Problem

To illustrate the challenge, let’s review an example result set from a DB2 SQL query. You might initially get results like this:

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

This result set includes multiple rows for the same item (e.g., 41031052-1), each with potentially different values in the DASHONLY column. Your goal is to modify your SQL statement so that you only display one row for each unique item number, depending on the criteria defined.

Desired Result Set

Here's how you want your result set to look:

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

The Solution: Using ROW_NUMBER()

To achieve this desired output, you can use the ROW_NUMBER() function in your SQL query. The ROW_NUMBER() function assigns a unique sequential integer to rows within a partition of a result set, which can help you isolate duplicates based on your criteria.

Here's a modified version of your SQL query that incorporates this strategy:

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

Breakdown of the Query

Subquery Creation: The SQL starts with a subquery that retrieves the necessary columns, including the item number (which is trimmed and any unnecessary spaces replaced) and the DASHONLY values.

Row Numbering: The crucial part is the use of ROW_NUMBER(). We partition the results by the item number and order it based on whether the DASHONLY column is NULL. This gives priority to entries with dash numbers.

Selecting Unique Rows: After defining the rows with their numbers, we simply filter for rn = 1, effectively keeping only the first entry for each partition.

Ordering Results: Finally, we order the results by the item number for a clean output.

Conclusion

By using ROW_NUMBER() in combination with partitioning and an ORDER BY clause, you can effectively eliminate duplicates from your SQL result set in DB2. This method not only streamlines your data but also ensures that you're always working with a concise and meaningful dataset. Happy querying!

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