Скачать или смотреть How to Conditionally Call Procedures in Prepared Statements in PostgreSQL

Learn how to use PL/pgSQL to conditionally call procedures in prepared statements when working with PostgreSQL. Code examples included!
---
This video is based on the question https://stackoverflow.com/q/67274284/ asked by the user 'Cemre Mengü' ( https://stackoverflow.com/u/586986/ ) and on the answer https://stackoverflow.com/a/67276127/ provided by the user 'eshirvana' ( https://stackoverflow.com/u/1367454/ ) 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: How to conditionally call procedure in prepared statement?

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.
---
How to Conditionally Call Procedures in Prepared Statements in PostgreSQL

In the world of databases, handling conditional logic within SQL statements can lead to complex but essential operations. If you've ever faced the challenge of wanting to call different stored procedures based on the input parameters in a single SQL statement, you're not alone! This guide will uncover the solution for conditionally invoking procedures in PostgreSQL using PL/pgSQL.

Understanding the Problem

You want to execute one of two different stored procedures based on a condition. For instance, if a certain status is 'Cleared', you want to call alarm_clear_check. Otherwise, you want to execute alarm_create. Generally, in SQL, this might seem straightforward, but procedures do not fit neatly into a single SQL statement when using standard SQL conditions. Here's a recap of the initial challenge:

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

The above attempt to use a CASE statement to call functions will not work as intended because you cannot call procedures within a CASE execution path.

The Solution: Using PL/pgSQL

The solution to your problem lies in using PL/pgSQL, PostgreSQL's procedural language, which allows you to execute more complex operations, including conditionally running code blocks based on the outcome of logical evaluations.

Step-by-Step Guide

Here’s how you can implement the solution using the PL/pgSQL DO statement:

Structure the DO Block: You start with a DO $$ statement to initiate a PL/pgSQL block.

Declare the Logic: Within this block, you can declare an IF statement to handle your conditional logic.

Call Procedures Based on Conditions: Depending on the condition, you call the appropriate procedure.

Here’s the exact code that you would use:

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

Breakdown of the Code:

DO $$: This starts the PL/pgSQL block.

BEGIN: The starting point of the logic; everything between BEGIN and END will be executed.

IF 'Cleared' = ? THEN: Checks if the condition is met, where ? represents the parameter supplied to the statement.

CALL procedure_name(...): Executes the desired stored procedure based on the outcome of the condition.

END IF;: Marks the end of the conditional logic.

END $$;: Concludes the PL/pgSQL block.

Key Benefits

Using PL/pgSQL in this scenario allows for greater flexibility and clarity. Here are some of the benefits you gain:

Complex Logic Handling: Easily incorporate complex business logic that can't be handled in standard SQL.

Reusability: Write your procedures once and call them wherever necessary.

Maintainability: Centralize your conditional logic into one neat block, making it easier to update and maintain.

Conclusion

While traditional SQL might restrict you in scenarios where procedure calls are dependent on conditions, PL/pgSQL opens the door for more intricate logic handling. By utilizing the above method, you can efficiently call different stored procedures based on the evaluation of conditions, further enhancing your application’s capabilities.

Now, you can confidently implement conditional procedure calling in your PostgreSQL database using PL/pgSQL. If you have any questions or additional cases you'd like to discuss, feel free to comment below!