Question

假设我有一个名为census的表，其中包含以下信息：

COUNTRY     PROVINCE    CITY        POPULATION
==============================================
USA         California  Sacramento  1234
USA         California  SanFran     4321
USA         Texas       Houston     1111
USA         Texas       Dallas      2222
Canada      Ontario     Ottawa      3333
Canada      Manitoba    Winnipeg    4444

我在国家/省级建立报告，它给了我以下内容：

SELECT country, province, SUM(population)
FROM census
GROUP BY country, province;

COUNTRY     PROVINCE    SUM(POPULATION)
=======================================
USA         California  5555
USA         Texas       3333
Canada      Ontario     3333
Canada      Manitoba    4444

我希望得到一个＆＃34;整体摘要＆＃34;行包含在报告中，以便最终结果如下：

COUNTRY     PROVINCE    SUM(POPULATION)
=======================================
USA         California   5555
USA         Texas        3333
Canada      Ontario      3333
Canada      Manitoba     4444
TOTAL                   16665

我熟悉ROLLUP，但我似乎无法找到一个能让我了解我想要的东西的组合。使用GROUP BY ROLLUP(country, province)包含我想要的总价值，但它还包含大量额外值，我并不关心。 GROUP BY ROLLUP(country), province

也是如此

我怎样才能完成＆＃34;总计＆＃34;记录？
我目前正在使用UNION ALL进行计算，并使用不同的GROUP BY重复第一个查询的90％，但由于第一个查询非常重要，因此结果是缓慢且难看的代码。

对于那些想要玩这个游戏的人来说，这是一个SQL小提琴：http://sqlfiddle.com/#!4/12ad9/5

Answer 1

这正是 GROUPING SETS 表达式的目的：

SELECT country, province, SUM(population)
FROM census
GROUP BY GROUPING SETS
   ( (country, province),        -- first group by country and province
     ()                          -- then by (nothing), i.e. a total grouping
   );

请参阅SQL-Fiddle

Answer 2

好的，我终于提出了两种灵活的方法，不会让我觉得自己像个可怕的程序员。

第一个解决方案涉及GROUPING SETS 我实际上要做的是将表达式分为两个不同的级别：一个在整体级别，一个在(country, province)级别。

如果我将查询分成两部分并使用UNION ALL，则一半会有GROUP BY country, province而另一半会缺少分组子句。如果我们愿意，未分组的部分也可以表示为GROUP BY ()。这将在一瞬间派上用场。

这给了我们类似的东西：

SELECT country, province, SUM(population)
FROM census
GROUP BY country, province
UNION ALL
SELECT NULL AS country, NULL AS province, SUM(population)
FROM census
GROUP BY ();

查询有效，但它不能很好地扩展。您需要进行的计算越多，重复自己的时间就越多。

通过使用GROUPING SETS，我可以指定我希望以两种不同的方式对数据进行分组：

SELECT country, province, SUM(population)
FROM census
GROUP BY GROUPING SETS( (country, province), () );

现在我们到了某个地方！但是我们的结果排怎么样？我们如何检测它并相应地标记它？那是GROUPING函数的来源。如果由于GROUP BY语句而导致列为NULL，则返回1。

SELECT
    CASE
        WHEN GROUPING(country) = 1 THEN 'TOTAL'
        ELSE country
    END AS country,
    province,
    SUM(population),
    GROUPING(country) AS grouping_flg
FROM census
GROUP BY GROUPING SETS ( (country, province), () );

如果我们不喜欢GROUPING SETS方法，我们仍然可以使用传统的ROLLUP，但稍作修改。

我们不是将每个列单独传递给ROLLUP，而是将列集合作为一个集合传递，将它们包含在括号中。这样就可以将列集视为单个组，而不是多个组。以下查询将为您提供与上一个相同的结果：

SELECT
    CASE
        WHEN GROUPING(country) = 1 THEN 'TOTAL'
        ELSE country
    END AS country,
    province,
    SUM(population),
    GROUPING(country) AS grouping_flg
FROM census
GROUP BY ROLLUP( (country, province) );

随意为自己尝试两种方法！
http://sqlfiddle.com/#!4/12ad9/102

Answer 3

在Oracle中，您可以使用having子句执行此操作：

SELECT coalesce(c.country, 'Total') as province, c.country, SUM(c.population)
FROM census c
GROUP BY ROLLUP(c.country, c.province)
HAVING c.province is not null or
       c.province is null and c.country is null;

Here是SQL小提琴。

Answer 4

首先想到的是在应用rollup后过滤掉小计：

SELECT *
FROM   (SELECT   country, province, SUM (population)
        FROM     census
        GROUP BY ROLLUP (country, province))
WHERE  province IS NOT NULL OR country IS NULL;

通过在GROUPING_ID子句中使用HAVING，您可以更紧凑地完成同样的事情：

SELECT   country,
         province,
         SUM (population)
FROM     census
GROUP BY ROLLUP (country, province)
HAVING   GROUPING_ID (country, province) <> 1

而且，正如@Anssssss指出的那样，您还可以使用WHERE子句中第一个答案中HAVING子句的条件：

SELECT   country, province, SUM (population)
FROM     census
GROUP BY ROLLUP (country, province)
HAVING   province IS NOT NULL OR country IS NULL

Answer 5

你可以使用联盟：

SELECT country, province, SUM(population)
FROM census
GROUP BY country, province
UNION
SELECT
   'Total', '', SUM(population)
FROM census

Answer 6

我想出了一个使用Union的SQL来将Total添加到结果的末尾。您可以看到query here

SELECT country, province, SUM(population) as population, 0 as OrderBy
FROM census
GROUP BY country, province
UNION
SELECT country, province, population, 1 as OrderBy FROM (
  SELECT 'Total' as country, '' as province, SUM(population) as population
  FROM census
)
ORDER BY OrderBy;

总结多个GROUP BY

6 个答案: