PostgreSQL聚合函数超出范围 [英] PostgreSQL aggregate function over range

问题描述

我正在尝试创建一个函数，该函数将找到 tsrange 的交集，但是我无法使它起作用：

I am trying to create a function that will find the intersection of tsrange, but I can't get it work:

CREATE AGGREGATE intersection ( tsrange ) (
    SFUNC = *,
    STYPE = tsrange
)

推荐答案

对您的尝试有两个修改。首先，我认为您不能将运算符用作SFUNC，因此您需要定义一个命名函数来执行交集，并使用它。

There are two modifications to your attempt. First, I don't think you can use an operator as the SFUNC, so you need to define a named function to do the intersection, and use that.

CREATE or REPLACE FUNCTION int_tsrange(a tsrange, b tsrange)
   returns tsrange language plpgsql as 
      'begin return a * b; end';

第二，范围的默认值为空范围-因此，交集始终为空。您需要将范围初始化为无限范围’[，]’才能开始聚合。聚合定义如下所示：

Secondly, the default value for a range is the empty range -- so the intersection will always be empty. You need to initialize the range to an infinite range '[,]' to begin the aggregate. The aggregate definition then looks like:

CREATE AGGREGATE intersection ( tsrange ) (
    SFUNC = int_tsrange,
    STYPE = tsrange,
    INITCOND = '[,]'
);

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