33. The system of claim 23 , wherein the second number of rows associated with the second index is determined by joining a set of primary keys of the second index with a primary keys index of the common table.
23. A system for improving a query in a multi-tenant database system, the system comprising: a processor; a network interface; and a computer-readable medium tangibly embodied with instructions to: receiving at a network interface of a server in a multi-tenant database system an original query transmitted to the multi-tenant database system by a user associated with a tenant, wherein the original query is associated with data accessible only by the tenant, and wherein the multi-tenant database system includes at least a first index and a second index, wherein the first index is a standard index and wherein the second index is a custom index to provide a private sharing paradigm within the multi-tenant database system that allows groups defined within one or more particular tenants to share information only among members of that group; retrieving, using a processor of the server, metadata associated with the data accessible only by the tenant in the multi-tenant database system, wherein at least a portion of the data accessible only by the tenant is stored in a common table within the multi-tenant database system; scanning a first index column to identify a first set of rows, wherein the first index column is selected based on the original query; scanning a second index column to identify a second set of rows, wherein the second index column is based on the original query; determining a third set of rows corresponding to an intersection of the first set of rows and the second set of rows; determining, using the processor, a tenant-selective query syntax, wherein determining comprises analyzing at least one of metadata generated from information about the tenant or metadata generated from the data accessible by the tenant; and generating, using the processor, an improved query using the query syntax, wherein the improved query is based upon the original query and the third set of rows.