db2_free_stmt() has been deprecated in favor of setting $stmt to an empty string. Example:
// close stmt resource and force it out of "scope"
$stmt = '';
Looks strange but it works.
(PECL ibm_db2 >= 1.0.0)
db2_free_stmt — Frees resources associated with the indicated statement resource
Frees the system and database resources that are associated with a statement resource. These resources are freed implicitly when a script finishes, but you can call db2_free_stmt() to explicitly free the statement resources before the end of the script.
A valid statement resource.
Returns TRUE on success or FALSE on failure.