Скачать или смотреть Solving the ORA-00933 Error in Oracle PL/SQL: How to Limit Rows in a Query

Discover the solution to the `ORA-00933` error when trying to limit rows in your Oracle PL/SQL cursor queries. Learn how to retrieve only the first two rows effectively.
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Understanding the ORA-00933 Error and How to Limit Rows in Oracle PL/SQL

If you're working with Oracle PL/SQL and trying to limit the number of rows returned by a query, you may have encountered the frustrating ORA-00933 error. This error typically arises when the SQL command is not properly formatted or ends unexpectedly. In this guide, we will explore how to effectively limit the rows returned from a query, specifically aiming to fetch only the first two rows from a dataset.

The Problem

You attempted to limit your cursor results by using the line:

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

However, this led to an error, specifically:

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

This error indicates that the SQL command executed is not understood due to incorrect syntax, highlighting the importance of following the SQL standards in Oracle.

The Solution

To retrieve only the first two rows from your query, you need to adjust the way you apply row limits in Oracle. Here's a step-by-step breakdown and the correct approach you should take:

1. Use a Subquery

Instead of trying to use the FETCH clause directly in your cursor, you should wrap your original query in a subquery. This allows you to first sort the results and then limit the number of rows returned.

2. Incorporate ROWNUM

You can use the ROWNUM pseudocolumn to limit the number of rows returned. Here's how you can implement it in your code:

Modified PL/SQL Code:

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

Explanation of the Code

Cursor Declaration: Here, CURSOR c IS defines a cursor that selects from a subquery.

Subquery: The inner query retrieves data from the book, publisher, and author tables, ordering them by title.

Limiting Rows: The outer query utilizes WHERE ROWNUM <= 2 to restrict the results to only the first two rows after the sorting is applied.

Output: Finally, we use DBMS_OUTPUT.put_line to display the information in a structured format.

Conclusion

By restructuring your query and using a subquery combined with the ROWNUM pseudocolumn, you can effectively limit the number of rows returned in PL/SQL without running into syntax errors like ORA-00933. Implementing these changes will provide you with a robust solution to fetch only the rows you need.

Now you can confidently manage your data queries in Oracle PL/SQL—limiting rows while ensuring your SQL syntax remains correct.