7

每个聚合的文档：

every(expression)：如果所有输入值都为真，则为真，否则为假

http://www.postgresql.org/docs/9.1/static/functions-aggregate.html

EVERY 在语义上等价于 COUNT(conditionIsTrue) = COUNT(*)

select person_id, 

    every(visited_site = 'http://stackoverflow.com') as visited_same_site_forever,

    count(case when visited_site = 'http://stackoverflow.com' then '^_^' end) 
    = count(*) as visited_same_site_forever2

from z
group by person_id
order by person_id

输出：

 person_id | visited_same_site_forever | visited_same_site_forever2 
-----------+---------------------------+----------------------------
        88 | f                         | f
     55327 | t                         | t
    256196 | f                         | f

数据源：

create table z(person_id int, visited_site varchar(100), datetime_visited timestamp);

insert into z values
(55327,'http://stackoverflow.com','Jan 1, 2010'),
(55327,'http://stackoverflow.com','Feb 14, 2012'),
(55327,'http://stackoverflow.com','May 1, 2012'),
(256196,'http://stackoverflow.com','February 1, 2012'),
(256196,'http://stackoverflow.com','February 2, 2012'),
(256196,'http://slashdot.org','May 2, 2012'),
(88,'http://theregister.co.uk','April 1, 2012'),
(88,'http://slashdot.org','April 2, 2012');
4

1 回答 1

6

模拟EVERY()和CASE_SUM()

事实上，这篇文章描述了如何EVERY()通过CASE和SUM()来模拟。以下两个语句是等价的：

SELECT EVERY(id < 10)
FROM book

SELECT CASE SUM(CASE WHEN id < 10 THEN 0 ELSE 1 END) 
         WHEN 0 THEN 1 
         ELSE 0 
       END
FROM book;

EVERY()窗口函数也是如此：

SELECT 
  book.*, 
  EVERY(title LIKE '%a') OVER (PARTITION BY author_id)
FROM book

SELECT
  book.*,
  CASE SUM(CASE WHEN title LIKE '%a' THEN 0 ELSE 1 END)
       OVER(PARTITION BY author_id)
    WHEN 0 THEN 1 
    ELSE 0
  END
FROM book;

SQL 标准

该SQL:2008标准提到了EVERY聚合函数：

10.9 <aggregate function>

[...]

<aggregate function> ::=
  COUNT <left paren> <asterisk> <right paren> [ <filter clause> ]
  | <general set function> [ <filter clause> ]
  | <binary set function> [ <filter clause> ]
  | <ordered set function> [ <filter clause> ]

<general set function> ::=
  <set function type> <left paren> [ <set quantifier> ]
  <value expression> <right paren>

<set function type> ::=
  <computational operation>

<computational operation> ::=
  AVG
  | MAX
  | MIN
  | SUM
  | EVERY
  | [...]

但“高级”SQL 标准特性通常不会由数据库实现。例如， Oracle 11g不支持它，SQL Server 2012也不支持。

但是，使用HSQLDB，您可能会更幸运。HSQLDB 2.x 非常符合标准，MySQL 也知道BIT_AND()聚合函数，它是 的非标准别名EVERY()，Postgres 也支持。

注意，有些数据库允许编写用户定义的聚合函数，所以你也可以EVERY()自己实现。

于 2012-05-02T08:38:09.557 回答