[bayesian_horse]

As far as I understand it a search engine like this is meant to perform well on "Human" queries that are hard to formalize.

SQL queries, asking for records based on something like field a has to contain b or something like that are easy to formalize and fulfill by an RDBMS. But the SQL queries get hairier and hairier when the query involves multiple fields or even multiple unrelated tables. Or free form text. And those queries are harder to index.

On top of all of that, Humans often want things sorted in an order that isn't straight-forward to express in SQL. What is "relevancy"? All of that can be done in SQL, but it's not what RDBMS engines shine at.