[英]Check constraint with dynamic parameters
我正在用PostgreSQL創建分區表。
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);
創建完上面的子表后,當我在下面的查詢中觸發時,它將掃描所有子表。
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);
從上面的查詢中,where子句中的log_time位於第42周。因此,該查詢應僅掃描“ tt_1_2015_week42”子表。 為什么上面的查詢會掃描所有3個子表?
用動態值檢查約束不起作用? 我們不能在Check約束中使用“ to_timestamp”功能嗎? 如何修改上面的子表檢查約束,以便查詢只能掃描第42周的表。
1)您的檢查條件缺少兩個相鄰分區之間的時間段。 例如,差距:
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
我會寫:
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)要獲得所需的內容,您需要一個選項constraint_exclusion設置為partition
(這應該是默認值)。
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