All partitions in a UNION ALL view must have a complete set of indexes defined for optimization to work.
Queries with DISTINCT will tend to run more slowly using a UNION ALL view than a base table.
Sybase IQ includes patented optimizations for UNION ALL views, including:
Split group by over union all view
Pushdown join into union all view
Should you need to adjust performance for queries that reference UNION ALL views, you may want to set the Join_Preference database option, which affects joins between UNION ALL views. For details of these options, see Chapter 5, “Database Options” in the Sybase IQ Reference Manual.
