Developing web applications in PHP often involves working with databases, where one common task is retrieving data from a database using the MySQLi extension. During this process, you may encounter the warning: "Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given". This article provides a detailed guide on how to identify and fix the cause of this warning.
Analyzing the Problem
The warning "Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given" indicates that the function mysqli_num_rows() was called with a parameter that is not a valid mysqli_result object, but a boolean value. This usually happens when the SQL query fails, and functions like mysqli_query() return FALSE instead of a mysqli_result object.
Step 1: Checking the SQL Query
The first step is to check the correctness of the SQL query. Make sure that the syntax of the query is correct and that all referenced tables and columns exist in the database.
$query = "SELECT * FROM table WHERE condition = 'value'";
$result = mysqli_query($connection, $query);
Step 2: Handling Errors during Query Execution
It is important to handle possible errors that may occur during query execution. If mysqli_query() returns FALSE, you should identify the cause of the query failure.
if (!$result) {
die("SQL query failed: " . mysqli_error($connection));
}
Step 3: Proper Usage of mysqli_num_rows() Function
After verifying that $result is a valid mysqli_result object, you can safely use mysqli_num_rows() to retrieve the number of rows in the result.
if (mysqli_num_rows($result) > 0) {
// Process the results
} else {
echo "No records found.";
}
Preventing Future Issues
- SQL Query Validation: Always carefully validate the syntax and logic of your SQL queries.
- Error Handling: Implement robust error handling for all database operations.
- Testing and Debugging: Use debugging and logging tools to identify and fix code errors.
Fixing the "Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given" warning boils down to ensuring that you pass a valid mysqli_result object to the mysqli_num_rows() function and properly handling errors when working with databases. By doing so, you'll ensure that your application is more robust and resilient to errors.
