Question

我正在postgres的hstore列中收集项目和版本号列表。我有兴趣看到100个最常见的键值对。例如，如果这是我的数据集：

"foo"=> "22", "foo"=> "33", "bar"=> "55", "baz"=> "77", "foo"=> "22"

我想知道"foo"=>"22"是我数据库中最常用的键/值对。让我们说一下，为了便于讨论表名为widgets且hstore列名为items的问题。

select ??? from widgets;

是否可以仅使用SQL获取顶部键值对的列表？

Answer 1

要将键/值对作为一个集合，相关函数为each()：

select * from each('a=>1,b=>2')

http://www.postgresql.org/docs/current/static/hstore.html#HSTORE-FUNC-TABLE

带限制的简单计数可以解决问题：

SELECT (item).key, (item).value, count(*) as count
FROM (SELECT each(items) as item FROM widgets) as t
GROUP BY (item).key
ORDER BY 2 DESC, (item).value
LIMIT 100

如果您只对密钥感兴趣，可以使用更简单的skeys()代替：

SELECT k, count(*) as count
FROM (SELECT skeys(items) as k FROM widgets) as t
GROUP BY k
ORDER BY 2 DESC, k
LIMIT 100

Answer 2

哦，这很容易。这里：

SELECT key, count(*) FROM
  (SELECT (each(h)).key FROM reports) 
    AS stat
GROUP BY key
ORDER BY count DESC, key
LIMIT 100;

Answer 3

当您在完整的键/值对之后，应执行以下操作：

select items, count(*) as cnt
from widgets
group by items
order by 2 desc
limit 100

在postgres中找到与Hstore最常见的键值对

3 个答案: