Problem with multiple prepared statements

Question

Here's the issue. I have a prepared statement, like this:

$select_something = $db->stmt_init();
$select_something->prepare ("
SELECT whatever 
FROM table
");
$select_something->execute();
$select_something->bind_result($whatever);

When alone - it works. When I add another one after it's execution it also works. But when I try to just first prepare them both:

$select_something = $db->stmt_init();
$select_something->prepare ("
SELECT whatever 
FROM table
");

and execute them later on:

$select_something->execute();
$select_something->bind_result($whatever);

the first statement gets executed, and the second one throws this error for both lines above:

*Warning: mysqli_stmt::execute() [mysqli-stmt.execute]: invalid object or resource mysqli_stmt*

Note, statements are named differently ($select_something and $select_something_else), I just thought it's needless to repeat the code.

Thanks!

Answer 1

Note that the mysqli extension has been replaced by PDO, which is simpler to use and better behaved. You should use it rather than mysqli. If you need a PDO tutorial, try "Writing MySQL Scripts with PHP and PDO". Even if you switch, you may still wish to figure out what is going wrong, in which case read on.

That particular error simply means you're not dealing with a mysqli_stmt in $select_something or $select_something_else. Functions in many extensions (especially DB extensions) return false when they fail, rather than a resource or object. That's probably what's happening here. Follow proper error handling procedure by testing the return value of functions that could fail. Use mysqli::error to get a description of why a MySQLi function/method is failing.

You may be running across a limitation of mysqli and the MySQL driver: the lower level mysql_use_result() or mysql_store_result() must be called on results before they can be used. By default, mysqli_stmt::execute probably calls mysql_use_result, which means the old result must be closed before a new query is run (which is mentioned in the documentation for mysqli::query()). Proper application of mysqli_stmt::store_result may fix the problem.

Note that you shouldn't need to call mysqli::stmt_init(), which is present (as mysqli_stmt_init) to support procedural programming. Instead, you can use mysqli::prepare().