I am trying to use the mysql_fdw with several MySQL tables that contain BLOB and LONGBLOB fields. I mapped these fields to BYTEA and TEXT fields in the corresponding Postgres foreign table. Queries ...

this is wrong because in 64 bit "unsigned long" will be 8 bytes, not 4 bytes. So, ~zero will be 0xFFFFFFFFFFFFFFFF instead of 0xFFFFFFFF as written in MySQL documentation.