How to pushdown filters to a view's group by clause? - postgresql

Question

We have a third party BI tool on the project that can only add a where clause with specified filters on a table/view select. We use a set of 4 source tables, they have indexes for columns that can be filtered using BI's UI. We have a view for each table that do grouping by indexed columns and add 1 additional column. Then we have another view that joins all the data from those 4 views using index columns, that is a view that is queried from our BI's UI, BI adds where clause to queries.
The problem is indexes on source tables are not utilized, filters are not pushed down on the level of tables, instead they are applied at the very end. We can't use Set Returning Function, all our BI tool can do is just select from table\view and add a where clause.
We thought about intercepting a select's where condition in Pg but I'm not sure is it possible. Or maybe it's possible to hint a optimizer that filters need to be pushed down. We can query source tables directly without using views but it will multiply a number of data sources\elements on UI which is not desirable. Is there any other ways we can solve it in PostgreSQL?
Update 1
Bellow examples of schemas/queries we use for our tables and views
CREATE TABLE source_table_1
(
dim1 VARCHAR(255) NOT NULL,
dim2 VARCHAR(255) NOT NULL,
dim3 VARCHAR(255) NOT NULL,
meausre1 Bigint NOT NULL,
meausre2 Bigint NOT NULL,
meausre3 Bigint NOT NULL
);
CREATE INDEX ON uc13_failures_by_cell (dim1, dim2, dim3);
... another 3 tables
CREATE OR REPLACE VIEW view1 AS
SELECT
"type1" as type,
dim1,
dim2,
dim3,
sum(meausre1) AS meausre1,
sum(meausre2) AS meausre2,
sum(meausre3) AS meausre3
FROM source_table_1
GROUP BY 1, 2, 3, 4;
... another 3 views
CREATE OR REPLACE VIEW view_uinion AS
SELECT
coalesce(view1.dim1, view2.dim1, view3.dim1, view4.dim1) AS dim1,
... two other dims
view1.meausre1 AS meausre1_1,
view2.meausre1 AS meausre2_1,
view3.meausre1 AS meausre3_1,
view4.meausre1 AS meausre4_1,
... two meausres
FROM view1
FULL JOIN view2 ON
view1.dim1 = view2.dim1 AND
view1.dim2 = view2.dim2 AND
view1.dim3 = view2.dim3 AND
FULL JOIN view3 ON ...
FULL JOIN view4 ON ...
WHERE -- this is were filters on dims are inserted
;

Answer 1

You cannot push a WHERE condition into a full outer join.
See this example:
CREATE TABLE a(id integer NOT NULL, a1 integer NOT NULL);
INSERT INTO a VALUES (1, 20), (2, 20);
CREATE TABLE b(id integer NOT NULL, b1 integer NOT NULL);
INSERT INTO b VALUES (2, 30), (3, 30);
SELECT *
FROM a
FULL JOIN b USING (id)
WHERE b1 = 30;
id | a1 | b1
----+----+----
2 | 20 | 30
3 | | 30
(2 rows)
SELECT *
FROM a
FULL JOIN (SELECT *
FROM b
WHERE b1 = 30) AS b_red
USING (id);
id | a1 | b1
----+----+----
1 | 20 |
2 | 20 | 30
3 | | 30
(3 rows)
So you would have to modify the underlying queries/views.
If you used inner joins, it would not be a problem.