Postgres LIKE唯一約束可能嗎？

我是Postgres的新用戶，正在使用pgAdmin III創建表（metrics_reaches）。Postgres LIKE唯一約束可能嗎？

在我的表中，我有一個insertion_timestamp的時間戳與時間編排類型列。

我想創建一個UNIQUE約束，該約束在其他字段中僅檢查insertion_timestamp的日期部分，而不是時間。

有沒有辦法做到這一點？這是我的腳本現在的樣子（請參閱最後的CONSTRAINT）。

-- Table: metrics_reaches 

-- DROP TABLE metrics_reaches; 

CREATE TABLE metrics_reaches 
(
    organizations_id integer NOT NULL, 
    applications_id integer NOT NULL, 
    countries_id integer NOT NULL, 
    platforms_id integer NOT NULL, 
    ... 
    insertion_timestamp timestamp with time zone NOT NULL, 
    id serial NOT NULL, 
    CONSTRAINT metrics_reaches_pkey PRIMARY KEY (id), 
    CONSTRAINT metrics_reaches_applications_id_fkey FOREIGN KEY (applications_id) 
     REFERENCES applications (id) MATCH SIMPLE 
     ON UPDATE CASCADE ON DELETE CASCADE, 
    CONSTRAINT metrics_reaches_countries_id_fkey FOREIGN KEY (countries_id) 
     REFERENCES countries (id) MATCH SIMPLE 
     ON UPDATE CASCADE ON DELETE CASCADE, 
    CONSTRAINT metrics_reaches_organizations_id_fkey FOREIGN KEY (organizations_id) 
     REFERENCES organizations (id) MATCH SIMPLE 
     ON UPDATE CASCADE ON DELETE CASCADE, 
    CONSTRAINT metrics_reaches_platforms_id_fkey FOREIGN KEY (platforms_id) 
     REFERENCES platforms (id) MATCH SIMPLE 
     ON UPDATE CASCADE ON DELETE CASCADE, 
    CONSTRAINT metrics_reaches_organizations_id_key UNIQUE (organizations_id, applications_id, countries_id, platforms_id, insertion_timestamp) 
) 
WITH (
    OIDS=FALSE 
); 
ALTER TABLE metrics_reaches 
    OWNER TO postgres;

來源

2013-05-30 FilmiHero

嘗試CAST（）：

CONSTRAINT metrics_reaches_organizations_id_key UNIQUE (
    organizations_id, 
    applications_id, 
    countries_id, 
    platforms_id, 
    CAST(insertion_timestamp AS date) 
)

來源

2013-05-30 17:54:25

對弗蘭克的回答評論不適合在這裏，因此發佈爲單獨的答案。 –

這實在是弗蘭克的回答評論，但它是太長了評論框。

如果您正在偏執，你需要仔細觀察當地的時區與日期打交道時轉換：

bookings=> SET timezone='GMT'; 
SET 
bookings=> SELECT now() at time zone 'GMT', (now() at time zone 'GMT')::date, now(), now()::date; 
     timezone   | timezone |    now    | now  
---------------------------+------------+------------------------------+------------ 
2013-05-30 19:36:04.23684 | 2013-05-30 | 2013-05-30 19:36:04.23684+00 | 2013-05-30 
(1 row) 

bookings=> set timezone='GMT-7'; 
SET 
bookings=> SELECT now() at time zone 'GMT', (now() at time zone 'GMT')::date, now(), now()::date; 
      timezone   | timezone |    now    | now  
----------------------------+------------+-------------------------------+------------ 
2013-05-30 19:36:13.723558 | 2013-05-30 | 2013-05-31 02:36:13.723558+07 | 2013-05-31

現在，PG是足夠聰明，知道這是一個問題，如果你嘗試創建帶有日期蒙上了約束，那麼你應該看到：

ERROR: functions in index expression must be marked IMMUTABLE

如果嘗試申請後施放「在時間區」，那麼它確實是不變的，你可以有你的約束。

當然，其他選項是將轉換包裝在一個函數中，並將該函數標記爲不可變。如果你要這樣對系統撒謊，不要抱怨當你的數據庫從現在起每年表現異常。

來源

2013-05-30 19:45:55

Postgres LIKE唯一約束可能嗎？

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