Скачать или смотреть Retrieving Multiple Results in PLSQL Using Loops

Discover how to effectively retrieve multiple results from a table using PLSQL, mimicking SQL Server's looping structure with recursive CTEs.
---
This video is based on the question https://stackoverflow.com/q/64957445/ asked by the user 'Irakli Salia' ( https://stackoverflow.com/u/12531906/ ) and on the answer https://stackoverflow.com/a/64957517/ provided by the user 'Gordon Linoff' ( https://stackoverflow.com/u/1144035/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Is it possible to loop in PLSQL to retrieve several results from one table based on variable?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Retrieving Multiple Results in PLSQL Using Loops

When working with databases, you often need to query for multiple results from a single table based on variable conditions. This requirement presents a challenge, especially when transitioning from SQL Server to PLSQL. In this guide, we will explore how to replicate SQL Server loop structures in PLSQL, utilizing techniques like recursive Common Table Expressions (CTEs) to achieve the desired outcome.

The Challenge

Let’s consider a scenario in SQL Server where you want to retrieve multiple records from the employees table based on a range of employee_id. The solution typically involves a loop that increments a counter variable until it reaches a specified limit. Here’s how such a loop looks in SQL Server:

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

In the example above, the counter starts from 100 and goes up to 105, allowing the selection of several employee records corresponding to those IDs. However, if you’re looking to implement a similar functionality in PLSQL, the method differs slightly.

The Solution: Using a Recursive CTE

In PLSQL, rather than using a traditional loop, you can employ a recursive CTE, which efficiently generates the necessary sequence of numbers and retrieves the corresponding employee records directly. The following code demonstrates this approach:

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

How It Works

Recursive CTE Initialization:

The CTE named n starts with a base value of 100. The FROM dual clause is a placeholder in Oracle used for selecting a single row.

Incrementing the Counter:

Using the UNION ALL clause allows for recursive calls, incrementing the counter by one each time until it reaches 105.

Joining with Employees Table:

The CTE result is then joined with the employees table on the employee_id, effectively retrieving all necessary records in one query.

Advantages of This Approach

Efficiency: By avoiding a loop, the recursive CTE can process the results in a single query, resulting in better performance and cleaner code.

Simplicity: This method reduces complexity, making the code easier to read and maintain.

Conclusion

Transitioning from SQL Server to PLSQL may come with its unique set of challenges, especially when it comes to data retrieval techniques. However, by using a recursive CTE, you can effectively mimic looping behaviors and retrieve multiple results from a table based on variable conditions. This not only enhances performance but also improves code readability.

Now you can confidently approach similar problems in PLSQL, implementing efficient querying solutions that meet your data retrieval needs. Happy coding!