English
English
When connecting to the database using PHP, the connect() function (such as mysqli_connect() or PDO connection) returns successfully, which means that the database server has successfully accepted the connection request. However, even if the connection is successful, it is still possible that a specific database table cannot be accessed due to insufficient permissions. This is a common confusion for many developers when debugging database permission issues.
This article will analyze the causes of this situation in detail and provide ideas on how to troubleshoot and solve the problem of insufficient permissions.
The connect() function is only responsible for establishing the connection to the database server. It verifies whether the user's username and password are correct and whether the server is accessible.
But the permission control of database access is more fine-grained, including:
Does this user have permission to access a database
Is there any permission to read, write, or modify a table
Is there any permission to perform specific operations (such as stored procedures)
Therefore, successful connection is only the first step, and subsequent operations on database tables still require corresponding permission support.
<?php
$mysqli = new mysqli("m66.net", "username", "password", "database");
// Connection successfully
if ($mysqli->connect_errno) {
echo "Connection failed: " . $mysqli->connect_error;
exit();
}
// Try to access the table
$result = $mysqli->query("SELECT * FROM sensitive_table");
if (!$result) {
echo "Query failed，error message：" . $mysqli->error;
}
?>
In the above code, connect() does not report an error, but may appear when executing the query:
Query failed，error message：Access denied for user 'username'@'host' to database 'database'
or:
Query failed，error message：SELECT command denied to user 'username'@'host' for table 'sensitive_table'
Insufficient database user permissions <br> The user account permissions used for connection are incomplete. It is possible that the account is only authorized to connect to the server or access some databases, but is not authorized to access certain tables or perform queries.
Database permission settings are high granularity <br> Database permissions are usually assigned to databases, tables, columns, and even operation levels. Successful connection is just to verify the identity. The actual operation depends on the user's permissions on the specific object.
Connecting users is inconsistent with operating users <br> Sometimes, the connection to the database is successful, but the actual identity of the query is not the current user, which may cause permission problems due to internal calls such as stored procedures and triggers.
Use the database management tool or the command line to view the user's permissions:
SHOW GRANTS FOR 'username'@'host';
Confirm that the user has the correct permissions to the target database and tables, for example:
GRANT SELECT, INSERT, UPDATE ON database.sensitive_table TO 'username'@'host';
FLUSH PRIVILEGES;
Check whether the username, password and host used for the connection are correct to avoid connecting to the wrong account or database.
According to the needs, the user is assigned corresponding permissions to avoid excessive authorization but also ensure normal access.
Use the same account test permissions in the database management tool to confirm whether the table can be accessed.
Here is an example of using mysqli to connect to a database with PHP and deal with permission errors:
