How to view specific SQL error message when prepare() fails

Troubleshooting database operations is a very common task when developing PHP applications. Especially when using mysqli extension, we often use prepare() function to prepare SQL statements. However, sometimes prepare() may fail. How can we view the specific error information? The mysqli::stmt_init function can help us solve this problem and provide more detailed error information.

What is mysqli::stmt_init?

mysqli::stmt_init is a function used to initialize the mysqli_stmt object. It allows you to create a prepared statement object for executing SQL statements. Usually, we call prepare() function to prepare SQL statements before executing SQL queries. If prepare() fails, calling mysqli_error() directly may not get specific SQL error information.

Through stmt_init initialization of the statement object, we can view the cause of the failure and more detailed error information after calling prepare() .

Sample code: How to view prepare() error using mysqli::stmt_init

Here is a sample code that uses mysqli::stmt_init to handle SQL statement errors:

 <?php
// Database connection settings
$host = 'localhost';
$username = 'root';
$password = '';
$dbname = 'test_db';

// create MySQLi connect
$mysqli = new mysqli($host, $username, $password, $dbname);

// 检查connect是否成功
if ($mysqli->connect_error) {
    die("connect失败: " . $mysqli->connect_error);
}

// use stmt_init initialization SQL Statement Object
$stmt = $mysqli->stmt_init();

// Prepare SQL Statement
$sql = "SELECT * FROM non_existing_table WHERE id = ?";

// pass stmt_init Function View prepare() Error message on failure
if (!$stmt->prepare($sql)) {
    // prepare When failure，Output specific SQL error message
    echo "SQL mistake: " . $stmt->error;
} else {
    echo "SQL Prepare成功！";
}

// 关闭connect
$stmt->close();
$mysqli->close();
?>

Code parsing:

1. Create a database connection : First, create a connection to the database through new mysqli() . If the connection fails, the script terminates and the connection error message is output.

2. Initialize statement object : Create a statement object $stmt through mysqli::stmt_init() , which will be used to execute SQL queries.

3. Prepare SQL statements : Use the $stmt->prepare($sql) function to prepare the SQL statement. If prepare() fails, $stmt->error will return the failed error message, which we can troubleshoot through.

4. Output error message : If prepare() fails, the code will output specific SQL error message to help developers understand the root cause of the problem.

5. Close the connection : After the operation is finished, remember to close the database connection and release the resources.

Common reasons for handling prepare() errors

1. SQL Syntax Error : One of the most common causes of errors. If there is a problem with the syntax of the SQL statement, prepare() will fail and return an error message.

2. Table or field does not exist : prepare() will also fail if a non-existent table or field is used in the SQL query.

3. Database connection problem : When there is a problem with the database connection itself, it will also affect the execution of prepare() .

Through the stmt_init function, we can understand in detail the specific reasons for prepare() failure, thereby effectively troubleshooting errors.