tree 1e6920e2d17e9e0f41edb2d6a6e9dcee9505f880
parent 96485c0ec8366d04f08f5c9a72bbee5b47503d6e
author Oliver Lee <oliverlee@google.com> 1706556455 +0000
committer Julian Hyde <jhyde@apache.org> 1708998609 -0800

[CALCITE-6219] 'Must-filter' columns

A table can declare that some of its columns must be filtered
by implementing `interface SemanticTable`. If such columns
are not filtered in a WHERE or HAVING clause, the validator
throws.

There are several purposes of these columns, one of which is
to prevent expensive full-table scans (for example, reading
all Orders without restricting on orderDate).

Implementation is via the method
SqlValidatorNamespace.getMustFilterFields(). For a table
namespace, that method returns the declared must-filter
fields. For a query namespce, that method returns any
must-filter fields that have not been filtered in that query;
such fields become the responsibility of the enclosing query.

If a field is must-filter and is not in the SELECT clause of a
sub-query, that is also an error, because of course it is now
impossible for the enclosing query to filter it.

Close apache/calcite#3688

Co-authored-by: Julian Hyde <jhyde@apache.org>