Add parsing of `ANN OF` queries to the `select_statement` and
`indexed_table_select_statement` classes.
Add a placeholder for the implementation of external ANN queries.
Rename `should_create_view` to `view_should_exist` as it is used
not only to check if the view should be created but also if
the view has been created.
Co-authored-by: Dawid Pawlik <dawid.pawlik@scylladb.com>
Currently we create a view for every index, however
for currently supported custom index classes (vector_index)
that work is redundant, as we store the index in the external
service.
This patch adds a way for custom indexes to choose whether to
create a view when creating the index and makes it so that
for vector indexes the view is not created.
Currently, to describe an index we look at
a corresponding view. However for custom indexes
the view may not exist (as we are removing the views
from vector indexes). This commit adds a way for a custom
index class to override the default describing logic
and provides such an override for the vector_index
class.
In this patch we add an abstract class, "custom_index", with a validate() method.
Each CUSTOM INDEX class needs to implement a concrete subclass of custom_index
which is used to validate if this type of custom index class may be used,
and whether the optional parameters passed to it are valid.
We change the existing CUSTOM INDEX validation code to use this new mechanism.
Finally this patch implements one concrete subclass for vector index.
Before this patch, the custom index type "vector_index" was allowed,
but after this patch it gains more validation of its optional parameters
(we support 4 specific parameters, with some rules on their values).
Of course, the vector index isn't actually implemented in this patch,
we are just improving the validation of the index creation statement.
