Question

我的上下文是PostgreSQL 8.3

我需要加快这个查询，因为两个表都有数百万条记录。

对于表Call中的每一行，Trunks表中有两行。对于每个call_id，当trunk_id是两行中最低的trunk_id时，我想将值从trunks.trunk复制到calls.orig_trunk。 ...当trunk_id是两行中最高的trunk_id时，将值从trunks.trunk复制到calls.orig_trunk。

表格通话的初始内容：

Call_ID | dialed_number | orig_trunk | dest_trunk
--------|---------------|------------|-----------
1       | 5145551212    |    null    |   null
2       | 8883331212    |    null    |   null
3       | 4164541212    |    null    |   null

表格树干：

Call_ID | trunk_id | trunk
--------|----------|-------
1       | 1        |  116
1       | 2        |  9
2       | 3        |  168
2       | 4        |  3
3       | 5        |  124
3       | 6        |  9

表格通话的最终内容：

Call_ID | dialed_number | orig_trunk| dest_trunk
--------|---------------|-----------|----------
1       | 5145551212    |    116    |   9
2       | 8883331212    |    168    |   3
3       | 4164541212    |    124    |   9

我为每一列创建了索引。

update calls set orig_trunk = t2.trunk 
from ( select call_id,trunk_id from trunks 
     order by trunk_id ASC ) as t2 
where (calls.call_id=t2.call_id );

update calls set dest_trunk = t2.trunk 
from ( select call_id,trunk_id from trunks 
     order by trunk_id DESC ) as t2 
where (calls.call_id=t2.call_id );

有什么想法吗？

Answer 1

从发布的示例中，看起来正在执行许多不必要的更新。以下是获取您要查找的结果的查询示例：

select distinct c.call_id, c.dialed_number
      ,first_value(t.trunk) over w as orig_trunk
      ,last_value(t.trunk)  over w as dest_trunk
  from calls c
  join trunks t on (t.call_id = c.call_id)
  window w as (partition by c.call_id
               order by trunk_id
               range between unbounded preceding
                         and unbounded following
              )

如果没有分析功能，还有其他方法可以做到这一点，例如：

select x.call_id
      ,x.dialed_number
      ,t1.trunk as orig_trunk
      ,t2.trunk as dest_trunk
  from (select c.call_id, c.dialed_number
              ,min(t.trunk_id) as orig_trunk_id
              ,max(t.trunk_id) as dest_trunk_id
          from calls c
          join trunks t on (t.call_id = c.call_id)
          group by c.call_id, c.dialed_number
        ) x
  join trunks t1 on (t1.trunk_id = x.orig_trunk_id)
  join trunks t2 on (t2.trunk_id = x.dest_trunk_id)

试验看看哪种情况最适合您的情况。可能希望在加入列上编入索引。

如何处理结果集取决于应用程序的性质。这是一次性的吗？那么为什么不从结果集中创建一个新表：

CREATE TABLE trunk_summary AS
  SELECT ...

它在不断变化吗？经常访问吗？仅仅创建一个视图就足够了吗？或者可能基于结果集执行更新。也许一次可以更新范围。这实际上取决于，但这可能会有一个开始。

Answer 2

这是带有测试条件的最终代码作为注释。子查询非常高效和快速。但是测试表明，对表的分区对执行时间的影响要大于子查询的效率。在包含100万行的表中，更新需要80秒。在包含12百万行的表中，更新需要580秒。

update calls1900 set orig_trunk = a.orig_trunk, dest_trunk = a.dest_trunk   
from (select 
  x.call_id,
      t1.trunk as orig_trunk, t2.trunk as dest_trunk 
  from (select calls1900.call_id
              ,min(t.trunk_id) as orig_trunk_id
              ,max(t.trunk_id) as dest_trunk_id
          from calls1900
          join trunks t on (t.call_id = calls1900.call_id)
          -- where calls1900.call_id between 43798930 and 43798950
          group by calls1900.call_id
        ) x
  join trunks t1 on (t1.trunk_id = x.orig_trunk_id)
  join trunks t2 on (t2.trunk_id = x.dest_trunk_id)
  ) a

where (calls1900.call_id = a.call_id); -- and (calls1900.call_id between 43798930 and 43798950)<code>

从另一个表更新表多行

2 个答案: