Deleting selected records

You can try this:

PHP Code:

$this->db->where('title REGEXP "^[a-z]" ', NULL,FALSE);
$this->delete('mz'); 


Explanation:
Usually, the where function in the query builder class will accept 2 parameters: the field and the value.
But it also accepts a custom MySQL statement as the first parameter. Then you must set the second parameter to NULL, and add a third parameter to tell the query builder that it should not try to "escape" the query.