prefix

前提条件

支持的PolarDB PostgreSQL版的版本如下：

PostgreSQL 14（内核小版本14.10.18.0及以上）。

select version();

背景信息

字符串前缀匹配是一个常见的业务功能。例如，在电话应用中，运营商可能希望在用户输入电话号码前缀时，就能够检索出满足前缀匹配的电话号码的完整列表。PolarDB PostgreSQL版支持prefix插件用于实现字符串前缀匹配的功能。以下是一个最长前缀匹配的示例：

SELECT *
    FROM prefixes
    WHERE prefix @> '0123456789'
ORDER BY length(prefix) DESC
    LIMIT 1;

使用方法

创建插件

CREATE EXTENSION prefix;

创建表和索引

CREATE TABLE prefixes (
        prefix    prefix_range PRIMARY KEY,
        name      TEXT NOT NULL,
        shortname TEXT,
        status    CHAR DEFAULT 'S',

        CHECK( status IN ('S', 'R') )
);
COMMENT ON COLUMN prefixes.status IS 'S:   - R: reserved';

INSERT INTO prefixes (prefix, name, shortname) VALUES
('010001','COLT TELECOMMUNICATIONS FRANCE','COLT'),
('010002','EQUANT France','EQFR'),
('010003','NUMERICABLE','NURC');

CREATE INDEX idx_prefix ON prefixes USING gist(prefix);

进行前缀匹配

SELECT '123'::prefix_range @> '123456';
 ?column?
----------
 t
(1 row)

SELECT * FROM prefixes WHERE prefix @> '01000123';
 prefix |              name              | shortname | status
--------+--------------------------------+-----------+--------
 010001 | COLT TELECOMMUNICATIONS FRANCE | COLT      | S
(1 row)

可使用的操作符

prefix插件提供了一系列操作符，包括常规的<=、<、=、<>、>=和>操作符，它们的含义与字符串比较操作符相同。此外，还有@>（包含）、<@（被包含）、&&（重叠）、|（并集）以及&（交集）。

SELECT a, b,
       a <= b AS "<=", a < b AS "<", a = b AS "=", a <> b AS "<>", a >= b AS ">=", a > b AS ">",
       a @> b AS "@>", a <@ b AS "<@", a && b AS "&&"
   FROM (SELECT a::prefix_range, b::prefix_range
         FROM (VALUES('123', '123'),
                         ('123', '124'),
                         ('123', '123[4-5]'),
                         ('123[4-5]', '123[2-7]'),
                         ('123', '[2-3]')) AS t(a, b)) AS x;
    a     |    b     | <= | < | = | <> | >= | > | @> | <@ | &&
----------+----------+----+---+---+----+----+---+----+----+----
 123      | 123      | t  | f | t | f  | t  | f | t  | t  | t
 123      | 124      | t  | t | f | t  | f  | f | f  | f  | f
 123      | 123[4-5] | t  | t | f | t  | f  | f | t  | f  | t
 123[4-5] | 123[2-7] | f  | f | f | t  | t  | t | f  | t  | t
 123      | [2-3]    | t  | t | f | t  | f  | f | f  | f  | f
(5 rows)

SELECT a, b, a | b AS UNION, a & b AS INTERSECT
   FROM (SELECT a::prefix_range, b::prefix_range
         FROM (VALUES('123', '123'),
                         ('123', '124'),
                         ('123', '123[4-5]'),
                         ('123[4-5]', '123[2-7]'),
                         ('123', '[2-3]')) AS t(a, b)) AS x;
    a     |    b     |  UNION   | INTERSECT
----------+----------+----------+-----------
 123      | 123      | 123      | 123
 123      | 124      | 12[3-4]  |
 123      | 123[4-5] | 123      | 123[4-5]
 123[4-5] | 123[2-7] | 123[2-7] | 123[4-5]
 123      | [2-3]    | [1-3]    |
(5 rows)