To adjust performance for queries that reference UNION ALL views, set the JOIN_PREFERENCE option, which affects joins between UNION ALL views.
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.
SAP Sybase IQ includes optimizations for UNION ALL views, including:
Split GROUP BY over UNION ALL view
Push-down join into UNION ALL view
A UNION can be treated as a partitioned table only if it satisfies all of the following constraints:
It contains only one or more UNION ALL.
Each arm of the UNION has only one table in its FROM clause, and that table is a physical base table.
No arm of the UNION has a DISTINCT, a RANK, an aggregate function, or a GROUP BY clause.
Each item in the SELECT clause within each arm of the UNION is a column.
The sequence of data types for the columns in the SELECT list of the first UNION arm is identical to the sequence in each subsequent arm of the UNION.