How to Fix 'OUT or INOUT argument...is not a variable' Error When Calling Stored Procedures with PDO?

Calling Stored Procedure with Out Parameter Using PDO: Resolved Bug

Despite following the PDO manual, you may encounter an "OUT or INOUT argument...is not a variable" error when calling a stored procedure with an output parameter. This is likely due to a bug in earlier versions of PHP and MySQL.

To resolve this issue, implement the following workaround:

1. In the stored procedure, add a SELECT statement for the output parameter. For example:

DELIMITER //  
CREATE PROCEDURE `proc_OUT` (OUT var1 VARCHAR(100))  
BEGIN  
    SET var1 = 'This is a test';  
    SELECT var1;  -- Select added to retrieve the output parameter
END //  

2. In your PHP code, use the normal PDO execute() method to call the stored procedure without binding the output parameter:

$stmt = $db->prepare("CALL proc_OUT(?)");
$stmt->bindParam(1, $return_value, PDO::PARAM_STR, 4000);
$stmt->execute();

3. After executing the stored procedure, retrieve the output parameter using a separate query() call:

$result = $db->query("SELECT var1 FROM proc_OUT");
foreach ($result as $row) {
    echo $row['var1'];
}

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