org.jpox.store.rdbms.adapter.RDBMSAdapter.useUnionAll()
Union combines the results of two or more queries into a single result set. Union include only distinct rows and Union all may include duplicates. When using the UNION statement, keep in mind that, by default, it performs the equivalent of a SELECT DISTINCT on the final result set. In other words, UNION takes the results of two like recordsets, combines them, and then performs a SELECT DISTINCT in order to eliminate any duplicate rows. This process occurs even if there are no duplicate records in the final recordset. If you know that there are duplicate records, and this presents a problem for your application, then by all means use the UNION statement to eliminate the duplicate rows. On the other hand, if you know that there will never be any duplicate rows, or if there are, and this presents no problem to your application, then you should use the UNION ALL statement instead of the UNION statement. The advantage of the UNION ALL is that is does not perform the SELECT DISTINCT function, which saves a lot of unnecessary SQL Server resources from being using.
@return Whether to use UNION ALL instead of UNION