Using PG 9.0 and given the following definitions:
CREATE SEQUENCE test_code_id;
CREATE TABLE test_table
(
status character(1) NOT NULL DEFAULT 'C'::bpchar,
code_id integer NOT NULL DEFAULT nextval('test_code_id')
);
CREATE INDEX test1
ON test_table
USING btree
(status, code_id);
CREATE OR REPLACE FUNCTION status_to_flag(status character)
RETURNS integer AS
$BODY$
DECLARE flag integer;
BEGIN
CASE status
WHEN 'C' THEN
flag = 1;
WHEN 'U' THEN
flag = 2;
WHEN 'D' THEN
flag = 3;
ELSE
CASE
WHEN status SIMILAR TO '[0-9]+' THEN
flag = CAST(status as integer);
ELSE
flag = 0;
END CASE;
END CASE;
RETURN flag;
END;
$BODY$
LANGUAGE plpgsql
CREATE OR REPLACE VIEW test_view1 AS
SELECT status_to_flag(test_table.status) AS flag,
test_table.code_id
FROM test_table;
CREATE OR REPLACE VIEW test_view2 AS
SELECT *
FROM test_view1
WHERE test_view1.flag = 1;
CREATE OR REPLACE VIEW test_view3 AS
SELECT status_to_flag(test_table.status) AS flag,
test_table.code_id
FROM test_table
WHERE test_table.flag = 1;
--To populate the table, copy / paste the following lines multiple times:
insert into test_table (status) VALUES ('C');
insert into test_table (status) VALUES ('D');
insert into test_table (status) VALUES ('U');
--A sequential scan is performed when a query is run against test_view2 such as:
SELECT * from test_view2
WHERE code_id > 10000
AND code_id < 10010;
--Whereas, if you run the same query against test_view3 the index is used:
SELECT * from test_view3
WHERE code_id > 10000
AND code_id < 10010;
As our tables / views are obviously a lot more complicated that the examples
above this causes up problems as we have to create all views to point directly
to the table rather than deriving them from other views.
Any ideas?
Regards,
Russell Keane
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