MySQL, check if foreign key is assigned to any table

Question

I have a table called files Additionally, I have over 100 tables in which I use associations/foreign keys file_id

How do I get all files that do not have an existing association (that is, the file is not attached to any table)?

Answer 1

I usually do this in bash (it might be possible to use SQL, but I'm not sure which table)

table_names=`echo "show tables"|mysql database_name -q -s|grep -v "show tables"`
for table in $table_names
do
  echo $table
  mysqldump database_name $table |grep file_id
done;

Then you will see something related to file_id in each table.