One post tagged with "sql"

One of the most interesting parts of building CamusDB is the query optimizer. It might also be one of the most complex pieces of machinery in the whole database.

At first, a query optimizer sounds simple: receive a SQL query and decide how to run it. But the more features a database supports, the harder that decision becomes. A query can use a table scan, an index lookup, an index range scan, a hash join, a merge join, a nested loop join, a sort, an aggregate, a derived table, or a subquery. Each option can be correct, but not every option is fast.

The optimizer's job is to choose a good plan before the query runs.