https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-key.html https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-k... Documentation for 5.7 says

https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-key.html https://dev.mysql.com/doc/refman/5.7/en/constraint-foreign-k... Documentation for 5.7 says it does create indexes for FKs automatically if one isn't created. > MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created.