In InterBase, you can't create a VIEW containing UNION. Actually
this is not 100% true, because engine supports such views. The
problem is bug in DSQL (Dynamic SQL) parser, which barfs at 'UNION'
keyword in 'CREATE VIEW' constructs. Since InterBase does
not allow DDL statements in stored procedures, the only way to
create such view currently is to write ESQL (Embedded SQL) code
and preprocess it with gpre, embedded SQL code preprocessor.
This is possible because gpre handles parsing by itself,
compiling directly into BLR.
