About Join Access
Indexes are an extremely important component of any join. This does not apply to global temporary trace tables, which can neither have indexes nor be joined to other tables. See “CREATE GLOBAL TEMPORARY TRACE TABLE” in SQL Data Definition Language Detailed Topics for details.
If, after implementing primary indexes for tables that are frequently joined, you detect significant performance issues when those tables are joined, you might want to reconsider your index column choices, particularly for commonly joined column sets in large tables. You might also want to consider adding additional columns to an existing index, depending on what your EXPLAINs for the query look like.