Скачать или смотреть Understanding mysqli_stmt::num_rows() Returning the Wrong Value in PHP

Discover why `mysqli_stmt::num_rows()` might return 0 when you expect a different value and learn how to fix it efficiently.
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This video is based on the question https://stackoverflow.com/q/80292/ asked by the user 'Steven Oxley' ( https://stackoverflow.com/u/3831/ ) and on the answer https://stackoverflow.com/a/80400/ provided by the user 'Nathan Strong' ( https://stackoverflow.com/u/9780/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing the Mystery of mysqli_stmt::num_rows() Returning 0 in PHP

When working with PHP and MySQL, especially using the mysqli extension and prepared statements, developers occasionally encounter baffling issues. One common problem is when the mysqli_stmt::num_rows() function returns 0, even when there are actual results available from the query. This post aims to clarify why this happens and how to resolve it.

The Problem: Unexpected Return Value

We start with a scenario where you have written a database handler class in PHP using mysqli prepared statements. You send a query to the database expecting to retrieve a value, yet upon checking with num_rows(), you receive 0.

Here’s a Sample Code:

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

Expected vs. Actual Output

Expected Result: 1name

Actual Result: 0name

So why is num_rows() returning 0 despite fetching a result?

The Solution: Adjusting the Order of Function Calls

The crux of the problem lies in the order in which the functions are called. The num_rows() function provides the number of rows in the result set, which may not be accurate after fetching results. To get the correct count, you should store the result before binding and fetching the values.

Revised Code Implementation

Here's the corrected version of the code:

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

Key Takeaways

Order Matters: Always call store_result() before bind_result() and fetch() when using mysqli_stmt::num_rows().

Understanding num_rows(): It reports the number of rows in the result set before processing the fetched data.

By adjusting the code structure and calling store_result() prior to using num_rows(), you should observe the expected behavior, in which num_rows() returns 1 for the existing data.

Conclusion

When dealing with the mysqli extension in PHP, understanding how various methods interact is crucial. Such small adjustments can help avoid confusion and improve your database handling code's reliability.

If you find yourself dealing with similar issues, remember to check the function order, as it can often hold the key to resolving seemingly inexplicable behaviors.