1. A computer-implemented method, comprising: receiving, by a computing device, a query for which one or more indexes are to be recommended, the query including one or more expressions; identifying, by the computing device, an expression in the query; generating, in the computing device, a set of column statistics related to the expression, and storing the set of column statistics in a memory; identifying one or more candidate function-based indexes associated with the query based, at least in part, on the set of column statistics; generating a set of function-based index statistics related to the one or more candidate function-based indexes; and recommending a candidate function-based index based, at least in part, on the set of function-based index statistics.