In PostgreSQL 14 or later, OIDs of aggregate functions are
described in fmrgoids.h, but that in PostgreSQL 13 doesn't
contain aggregate function OIDs. Therefore, we get the OID
by passing the function name and arg type to to_regprocedure().
When a base table is truncated, the view content will be empty if the
view definition query does not contain an aggregate without a GROUP clause.
Therefore, such views can be truncated.
Aggregate views without a GROUP clause always have one row. Therefore,
if a base table is truncated, the view will not be empty and will contain
a row with NULL value (or 0 for count()). So, in this case, we refresh the
view instead of truncating it.
Built-in count, sum, avg are supported. We have not supported min/max
yet, but will support in future.
When an IMMV with any aggregates are defined, additional columns
are created for each aggregate function. Although such columns are
"hidden" in pgsql-ivm version, they are always visible for users
in the extension version.
refresh_immv(immv_name, with_data) is a function to refresh IMMV like
REFRESH MATERIALIZED VIEW command. It has two argument.
immv_name is incrementally maintainable materialized view's name, and
with_data is an option that is corresponding to the WITH [NO] DATA option.
When with_data is set false, the IMMV gets unpopulated.
One of differences between IMMVs unpopulated by this function and
normal materialized views unpopulated by REFRESH ... WITH NO DATA
is that such IMMVs can be referenced by SELECT but return no rows,
while unpopulated materialized views are not scanable.
The behaviour may be changed in future to raise an error when unpopulated
an IMMV is scanned.
createas.c and matview.c contain corresponding functions that are
defined in the same name files in the core version. pg_ivm.c contains
user interface functions and callback functions.
The file names are identical to those in the core code ( in pgsql-ivm
repository) and some codes are copied from it so that we can easily
compare the code between the extension and the core. That is because
we would like to apply features in this extension to the core as a new
feature in future. Also, we plan to adopt the core code change to the
extension to prevent the difference from being too far. However,
considering modularity or code-readability, it is possible that we may change this policy in future.
In passing, Makefile is also fixed and we don't need to use
USE_PGXS now.
This currently crashes the server: `SELECT create_immv(NULL, 'SELECT * FROM test');` . Marking the function STRICT will avoid calling it with NULL arguments.
Alternative would be check for NULLs in create_immv.
