Thanks for the advice; I had not come across the INSERT IGNORE command so that's massively useful. Here is my code (minus error messages):-
Might you be able to explain how to use the SELECT command to retrieve and insert the 'theatre_id' data (from pre-existing or newly-created entries in the 'theatre' table) into the 'theatreid' field (of the 'prodtheatre' table)?
$sql = "INSERT IGNORE INTO theatre SET
$theatreid = mysqli_insert_id($link); //OBTAINS NEWLY ACQUIRED theatre_id
$sql = "INSERT INTO prodtheatre SET
Thanks (I'm still a beginner)!