用动态参数检查约束

Question

I am creating partition table with PostgreSQL.

CREATE TABLE tt_parent
(
    id integer,
    log_time timestamp with time zone,
    server_id integer,
    name text,
    CONSTRAINT tt_parent_pkey PRIMARY KEY (id)
)

CREATE TABLE tt_1_2015_week42 (
 CHECK ( server_id = 1 AND log_time >= (to_timestamp('2015-42', 'IYYY-IW')) AND log_time <= (to_timestamp('2015-42', 'IYYY-IW') + '6 days'::interval)
) INHERITS (tt_parent);

CREATE TABLE tt_1_2015_week43 (
 CHECK ( server_id = 1 AND log_time >= (to_timestamp('2015-43', 'IYYY-IW')) AND log_time <= (to_timestamp('2015-43', 'IYYY-IW') + '6 days'::interval)
) INHERITS (tt_parent);

CREATE TABLE tt_1_2015_week44 (
 CHECK ( server_id = 1 AND log_time >= (to_timestamp('2015-44', 'IYYY-IW')) AND log_time <= (to_timestamp('2015-44', 'IYYY-IW') + '6 days'::interval)
) INHERITS (tt_parent);

After creating the above child table when i fire below query then it scan all the child table.

EXPLAIN SELECT * FROM tt_parent 
WHERE server_id = 1 
AND (log_time >= '2015-10-12 00:00:00'::TIMESTAMP WITH TIME ZONE) 
AND (log_time <= '2015-10-15 00:00:00'::TIMESTAMP WITH TIME ZONE);

From the above query, log_time in where clause is with week 42. So the query should scan only "tt_1_2015_week42" child table. Why above query scan all the 3 child tables ?

Check constraint with dynamic value does not work ? We can not use "to_timestamp" function inside Check constraint ? How to modify the above child table check constraint so that query can scan only week 42 table.

Answer 1

1) Your check-conditions missing periods between two neighbour partitions. For example, a gap:

from: to_timestamp('2015-42', 'IYYY-IW') + '6 days'::interval --2015-10-18 00:00:00
to:   to_timestamp('2015-43', 'IYYY-IW'))                     --2015-10-19 00:00:00

I would write:

CHECK (
    server_id = 1 AND
    log_time >= '2015-10-12'::timestamptz AND
    log_time < '2015-10-12'::timestamptz + interval '1 week' --'<' sign, not '<=' to avoid overlapping
)

2) To get what you want you need an option constraint_exclusion set to partition (this should be a default value).