[在SQL Server中使用CASE语句的最小MAX

Question

我有这样一张桌子。我要输入的所有国家名称，人口编号，以及如果MAX中的人口，则标记MAX，并类似地标记MIN。我已经在下面使用CASE语句在SQL Server中编写了查询。

/* MIN/MAX Population amongst the countries */
SELECT 
    country, population,
    CASE
        WHEN population == MIN(population) THEN "MIN"
        WHEN population == MAX(population) THEN "MAX" ELSE "NA"
    END as "pop_stats"
FROM
    countries_by_population;

Answer 1

Demo on db<>fiddle

首先，应该通过如下所示存储@Min_Population和@Max_Population

DECLARE @Min_Population decimal(18,2), @Max_Population decimal(18,2)
SELECT @Min_Population = MIN(population), @Max_Population = MAX(population)
FROM countries_by_population

[之后，您可以像这样比较每个项目的值（请注意，SQL中的字符用单引号而不是双引号封闭）

CASE
    WHEN population = @Min_Population THEN 'MIN'
    WHEN population = @Max_Population THEN 'MAX' ELSE 'NA'
END as pop_stats

完整查询

DECLARE @Min_Population decimal(18,2), @Max_Population decimal(18,2)
SELECT @Min_Population = MIN(population), @Max_Population = MAX(population)
FROM countries_by_population

SELECT country, population,
    CASE
        WHEN population = @Min_Population THEN 'MIN'
        WHEN population = @Max_Population THEN 'MAX' ELSE 'NA'
    END as pop_stats
FROM countries_by_population;

Answer 2

您可以使用窗口分析函数，例如DENSE_RANK()和ORDER BY population（默认）顺序中包含descending子句的ascending来通过从MIN返回值来确定MAX和1值以便分别在CASE语句中使用（DENSE_RANK()函数返回极值中ties发生情况下满足相关条件的一行以上]]

SELECT country, population,
       CASE
         WHEN DENSE_RANK() OVER ( ORDER BY population ) = 1 THEN 'MIN'
         WHEN DENSE_RANK() OVER ( ORDER BY population DESC ) = 1 THEN 'MAX' ELSE 'NA'
       END AS "pop_stats"
  FROM countries_by_population
 ORDER BY population DESC
顺便说一句，不要对导出的列值使用双引号，而应使用单引号。

Demo

Answer 3

使用over()使其成为没有分区的窗口函数：