In the books
In A Song of Ice and Fire, Long Table is spelled "Longtable". It is the seat of House Merryweather. House Merryweather are notable for providing one of the Hands of the King under Aerys II Targaryen, the Mad King, after Tywin Lannister's resignation. Lord Owen Merryweather was the Hand until the early stages of Robert's Rebellion, which he did not take seriously. For his laxity, Aerys stripped him of his lands and sent him into exile, replacing him with Lord Jon Connington of Griffin's Roost. After taking the Iron Throne, Robert Baratheon restored some of the lands to Owen's heirs, including Longtable. The current lord of the house, Orton, is married to the Lady Taena of the Free City of Myr.