Perform a search on a table or another with PHP

What I would like is the following: I have two tables, being tabelaA and tabelaB . I want the search term if not found in one table, be queried in another table. I do not know if there's anything you can do to put the two tables together or how it might happen. So in summary, if I type by cell, the search will return the data either from table A or from table B.