View flattening

When evaluating a statement that references a view, Derby internally transforms a view into a derived table. This derived table might also be a candidate for flattening into the outer query block.

A view or derived table can be flattened into the outer query block if all of the following conditions are met:
For example, given view v1(a,b):
SELECT Cities.city_name, Countries.country_iso_code
FROM Cities, Countries
WHERE Cities.country_iso_code = Countries.country_iso_code
and a SELECT that references it:
SELECT a, b
FROM v1 WHERE a = 'Melbourne'
after the view is transformed into a derived table, the internal query is
SELECT a, b
FROM (select Cities.city_name, Countries.country_iso_code
FROM Cities, Countries
WHERE Cities.country_iso_code = Countries.country_iso_code) v1(a, b)
WHERE a = 'Melbourne'
After view flattening it becomes
SELECT Cities.city_name, Countries.country_iso_code
FROM Cities, Countries
WHERE Cities.country_iso_code = Countries.country_iso_code
AND Cities.city_name = 'Melbourne'
Related concepts
Predicates pushed into views or derived tables