The single biggest disadvantage to Ingress is that it is sold and support by Computer Associates.
Ingress and MySQL are a night and day comparison though.
Ingress comes from the same base as Postgresql, and was originally designed more as a scientific / research database (i.e. it can store all kinds of fun mathematical types and do neat things with them.) and has triggers, transactions, and stored procedures.
MySQL was designed as a high speed data store with a SQL front end.
Ingress and other RDBMS like it can usually handle larger parallel load better, and lots of mixed reads and writes. Unfortunately, this means that it's not ever really zippy for joe casual user by himself, and MySQL flies in role of being user by a few people at a time, like in a small order entry system or something.
But if you have a choice, I'd pick Postgresql over Ingress now. They're similar enough, and Postgresql is a whole lot cheaper and better supported.
