返回在 Postgres 中最近的评级城市团队的函数

Question

假设我有表联盟（城市，球队）和排名（城市，评级）（除了评级是真实类型外，其他都是字符串）。排名中还有一些额外的城市不一定在联赛中。我正在尝试创建一个名为closestRating的函数，该函数将接收一个城市，并在函数参数中返回其城市与该城市的评分差距最小的球队的名称（意思不是它自己），或者如果我们正在寻找的城市也在联盟中，则返回与该城市参数对应的球队名称。（曼城在联赛和排名中都被定义为varchar（20））。

我的尝试有一些非常奇怪的语法错误

    CREATE FUNCTION closestRating (city varchar(20)) RETURNS VARCHAR(20) AS $$
    DECLARE minimum real;
    DECLARE rat real;
    BEGIN
        SET minimum = -1;
        FOR r.city, rating IN (SELECT r.city, r.rating FROM rankings r)
        LOOP
            IF city = r.city
            BEGIN
                SET rat = rating;
            END IF;
        END LOOP;
        FOR rating IN (SELECT r.city, r.rating FROM rankings r, league l WHERE r.city = l.city)
        LOOP
            IF minimum = -1 OR minimum < ABS(rat – rating)
            BEGIN
                SET minimum_dist = ABS(r – rating);
                SET rat = rating;
            END IF;
        END LOOP;
        RETURN (SELECT team from rankings, league WHERE rating = rat));
    END;
    $func$
    LANGUAGE plpgsql;   

Answer 1

给定此数据：

create table league (
    city varchar(20),
    team varchar(20)
);
create table rankings (
    city varchar(20),
    rating real
);
insert into rankings (city, rating) values
    ('citya', 1),('cityb', 1.1),('cityc', 1.01),('cityd', 1.102),('citye', 1.2)
;
insert into league (city, team) values
    ('citya', 'teama'),('cityc', 'teamc'),('citye', 'teame')
;

此查询将返回预期输出：

with given_city as (
    select rating, city
    from rankings
    where city = 'citya'
)
select l.team
from
    league l
    inner join
    rankings r using (city)
    cross join
    given_city gc
order by abs(r.rating - gc.rating)
limit 1
;
 team  
-------
 teama