Скачать или смотреть How to Use UNION ALL to Query Multiple Ranges in Oracle SQL

Learn how to run a single Oracle SQL query that counts rows across multiple ranges using `UNION ALL`. This guide will walk you through creating an efficient and effective solution.
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Efficiently Counting Rows Within Multiple Ranges in Oracle SQL

When working with databases, you may encounter situations where you need to retrieve data that falls within specific ranges. For instance, if you're tracking serial numbers in a system, you might want to count how many serial numbers exist within several defined ranges, all in a single query. This guide will guide you through the process of achieving this in Oracle SQL using the UNION ALL clause.

The Problem at Hand

Let's say you have an Oracle table named my_tab that contains a column SERIALNR. You want to count how many entries lie within several ranges of serial numbers, such as:

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

You may start with a query that counts entries in a single range, but how do you extend that to include multiple ranges without running separate queries?

The Solution: Using UNION ALL

The best approach to gather counts from multiple ranges in a single SQL query is to use the UNION ALL clause. This allows you to combine the results of multiple SELECT statements into one result set. Below is a structured breakdown of how to implement this.

Step-by-Step Query Construction

Basic Structure: Start by creating a SELECT statement for each range you need to query.

Count and Label: For each range, use the COUNT function to calculate the number of rows, and consider labeling each range for clarity.

Combine with UNION ALL: Join all the SELECT statements using UNION ALL to ensure all data from the different ranges appear in your results.

Sample SQL Query

Here’s how your complete query would look:

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

Important Notes

Data Type: Ensure that the SERIALNR column is of type NUMBER. You do not need to quote numerical values in the BETWEEN clause.

Performance: Using UNION ALL is efficient for combining results without eliminating duplicates, making it ideal for counting distinct rows as we have done here.

Conclusion

By leveraging the UNION ALL clause in Oracle SQL, you can efficiently query and count records across multiple ranges in one go. This not only simplifies your SQL queries but also enhances readability and maintains performance.

Feel free to implement this approach in your database queries, and you’ll find it a time-saving technique for similar use cases!