--pg支持范围类型
• int4range — Range of integer
• int8range — Range of bigint
• numrange — Range of numeric
• tsrange — Range of timestamp without time zone
• tstzrange — Range of timestamp with time zone
• daterange — Range of date
--范围时间戳
CREATE TABLE reservation (room int, during tsrange);
--插入范围内时间
INSERT INTO reservation VALUES
(1108, '[2010-01-01 14:30, 2010-01-01 15:30)');
--正无空大，负无穷小 -infinity 代表无穷小
INSERT INTO reservation VALUES
(1109, '[2010-01-01 14:30,"infinity" )'),(1110, '["-infinity",2010-01-01 14:30)');
postgres=# select * from reservation ;
room | during
------+-----------------------------------------------
1108 | ["2010-01-01 14:30:00","2010-01-01 15:30:00")
1109 | ["2010-01-01 14:30:00",infinity)
1110 | [-infinity,"2010-01-01 14:30:00")
-- Containment 范围内是否包含某一个值
SELECT int4range(10, 20) @> 3;
-- Overlaps 两个范围是否有重叠
SELECT numrange(11.1, 22.2) && numrange(20.0, 30.0);
-- Extract the upper bound 求范围的上限
SELECT upper(int8range(15, 25));
-- Compute the intersection 求两个范围的交集
SELECT int4range(10, 20) * int4range(15, 25);
-- Is the range empty? 判断范围是否为空
SELECT isempty(numrange(1, 5));
--每个范围类型都有一个与对应的构造函数，注意第三个参数说明其是全包围还是半包围
postgres=# SELECT int8range(1, 14, '(]');
int8range
-----------
[2,15)
postgres=# SELECT numrange(NULL, 2.2);
numrange
----------
(,2.2)
--用户也可以自定义范围类型，注意如果想要更好的使用GiST or SP-GiST索引，则需要定义一个差异化函数
--差异化函数要返回一个float8的值，并且其结果不能受字符集和排序规则的影响
--The subtype difference function takes two input values of the subtype, and returns their difference (i.e., X minus Y) represented as a float8 value
--the subtype_diff function should agree with the sort ordering implied by the selected operator class and collation
--创建差异化函数
CREATE FUNCTION time_subtype_diff(x time, y time) RETURNS float8 AS
'SELECT EXTRACT(EPOCH FROM (x - y))' LANGUAGE sql STRICT IMMUTABLE;
--创建自定义的范围类型
CREATE TYPE timerange AS RANGE (
subtype = time,
subtype_diff = time_subtype_diff
);
postgres=# SELECT '[11:10, 23:00]'::timerange;
timerange
---------------------
[11:10:00,23:00:00]
--可以对范围类型的表列创建 GiST 和 SP-GiST 索引。
--虽然对范围类型的表列可以创建 B-tree 和哈希索引，但不建议使用
--There is a B-tree sort ordering defined for range values, with corresponding < and > operators, but the ordering is rather arbitrary and not usually useful in the real world
CREATE INDEX reservation_idx ON reservation USING gist (during);
