Add front-end Search and Sort functionality to existing PHP pages -- 2

Hello, I have an existing website that automatically pulls data from a SQL database and displays it using PHP. I have some rudimentary sorting functionality, and I need to add full Sorting and Search functionality to this list. You can view the existing website at: [login to view URL] SORT: * Currently, the Sort functionality only applies to the current page of items (not the full list of items). This needs to be fixed. * You should be sure that if an item has a NULL value, it doesn't rank at the top of the sorted results. * The Sort functionality should "stack". So if you sort by column 1, and then sort by column 2, then column 1 will still be sorted but secondary to column 2. SEARCH: * The website currently doesn't have any search functionality, only placeholder form elements. * "Select" elements, such as 'Condition' and 'Manufacturer', should have the ability to simultaneously multi-select multiple values. * If a user leaves a value blank, it should be an "inclusive" search and not exclude that value from the search. I am happy to answer any questions you have about this project, such as the existing code and how it connects to my database. Thanks. This should be a relatively simple project. BUDGET: $50 - $80