Resolving the Trigger Problem in Oracle PL/SQL: Why Your Output Isn't Displaying

Discover how to effectively troubleshoot and resolve the issue when your Oracle PL/SQL trigger compiles but the output is not displayed as expected.
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This video is based on the question https://stackoverflow.com/q/66028217/ asked by the user 'K0K0S' ( https://stackoverflow.com/u/15133622/ ) and on the answer https://stackoverflow.com/a/66028786/ provided by the user 'Littlefoot' ( https://stackoverflow.com/u/9097906/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Trigger Problem in Oracle PL/SQL

You’re working on a trigger in Oracle PL/SQL that is meant to display messages whenever records are inserted, updated, or deleted in your database table, Zegarek. However, after compiling without any errors and performing an update, the output message fails to display. This can be frustrating, especially when the database confirms that the row was updated successfully. Here, we will explore the reasons behind this issue and how to resolve it effectively.

The Trigger Code

Let’s look at the trigger code you have written:

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The Issue

After performing your update command on the Zegarek table:

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Despite the database confirming the success of the update, you're not seeing the expected output message:

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The Solution: Enabling Output

The most likely reason for not seeing your output is that the server output is turned off by default in SQL*Plus or other environments. For the DBMS_OUTPUT.PUT_LINE to display messages, you need to enable it first.

Here’s How to Do It:

Enable Server Output: Run the following command before executing your update statement:

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This command instructs Oracle to display the output messages generated by your PL/SQL blocks.

Perform Your Update Again: Now, execute your update statement once again:

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Expect the Output: After running the update, you should now see:

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Conclusion

By ensuring that server output is enabled, you can effectively see the messages produced by your triggers and PL/SQL blocks. Remember that often, the simplest solutions can resolve technical hassles. Now that you know how to troubleshoot this issue, you can confidently utilize triggers to enhance your database functionalities in Oracle PL/SQL.

If you encounter similar problems in the future, always check if your output is enabled. Happy coding!

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