MySQL, check if foreign key is assigned to any table

Question

I have a table called files. Additionally, I have more than 100 tables in which I use association/foreign key file_id. How can I get all files for which no association exists (that is, the file is not attached to any table)?

P粉566048790 · Answer

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.

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