The IDL-SQL library allows you to easily execute SQL queries in any SQL database from IDL and retrieve the results of these queries as arrays in IDL (ITT, RSINC). This library does not use the IDL Dataminer extension, so you do not need a license for it. To access the database, this library uses JDBC.

The description of the library as well as IMPORTANT installation instructions are here http://code.google.com/p/idl-sql/wiki/README

There is another library to perform SQL queries from IDL, which doesn't use IDL-Java bridge, but requires compilation and only works for PostgreSQL database: https://github.com/segasai/pg_idl