The `spell_required` table
Table used to add restrictions for learning spells from trainer. Player can't learn spell 'spell_id' till he learns 'req_spell', when he loses 'req_spell' 'spell_id' will be lost too. Table is used also for profession specialisations as specialisations require profession of certain rank to learn.
Description of the fields
Spell ID from Spell.dbc, which require knowing `req_spell` to learn from trainer.
Spell ID from Spell.dbc, which is required to be known before `spell_id` can be learned from trainer.