You must be the owner of a table or the DBA to create, alter, or synchronize a join index that includes that table. If you are not the DBA, you need to be the owner of the table and have RESOURCE authority in order to create a join index.
For complete syntax, see CREATE TABLE statement, ALTER TABLE statement, LOAD TABLE statement, INSERT statement, and SYNCHRONIZE JOIN INDEX statement in Reference: Statements and Options. The sections that follow explain more about creating a join index.