6. A system for performing a database query in a relational database, the database query being carried out by a database engine and being based on user-defined search criteria, the system comprising: the relational database having a non-transitory computer-readable storage medium; a microprocessor programmed to: retrieve a number N of properties of a record within a main database table, the number N being higher than zero; create a search criteria option for each of the N properties; create a separate search criteria table for every search criteria option; create a separate index table for every search criteria table only once, wherein there is at least one common search criteria option between the index tables; present on a user-interface search criteria options for a user to select; select the search criteria options for forming a user-defined combination of a plurality of the search criteria options and associated indexes; and perform the database query based on the user-defined combination of the plurality of the search criteria options and the associated indexes.
6. A system for performing a database query in a relational database, the database query being carried out by a database engine and being based on user-defined search criteria, the system comprising: the relational database having a non-transitory computer-readable storage medium; a microprocessor programmed to: retrieve a number N of properties of a record within a main database table, the number N being higher than zero; create a search criteria option for each of the N properties; create a separate search criteria table for every search criteria option; create a separate index table for every search criteria table only once, wherein there is at least one common search criteria option between the index tables; present on a user-interface search criteria options for a user to select; select the search criteria options for forming a user-defined combination of a plurality of the search criteria options and associated indexes; and perform the database query based on the user-defined combination of the plurality of the search criteria options and the associated indexes. 8. The system according to claim 6 , wherein the user-defined combination is based on choosing at least one user-selectable combination function and is further based on providing the plurality of the search criteria options as parameters to the user-selectable combination function.