Question

如果我想在约会中添加5天，我可以使用INTERVAL函数执行此操作：

select create_ts + interval '5 days' from abc_company;

但是，我的表有一个名为num_of_days的字段，我想将它添加到我的create_ts中。像这样：

select create_ts + interval num_of_days || ' days' from abc_company;

这不起作用。我怎样才能在postgresql中完成这个？

Answer 1

只需将值乘以间隔：

select create_ts + num_of_day * interval '1' day 
from abc_company;

Answer 2

你只需要一个工作类型转换。这种是标准的SQL。

select current_timestamp + cast((num_of_days || ' days') as interval)
from abc_company;

这是PostgreSQL特有的另一种语法。

select current_timestamp + (num_of_days || ' days')::interval
from abc_company;

我不想尝试记住PostgreSQL支持的第三种类型转换，这是类似函数的语法。

select current_timestamp + "interval" (num_of_days || ' days')
from abc_company;

为什么呢？因为some function names have to be quoted; interval 就是其中之一。

此外，名称间隔，时间和时间戳只能在此使用如果它们是双引号的时尚，因为句法冲突。因此，使用类似函数的强制转换语法不一致，应该避免。

Answer 3

here is a function that I use:

scala> consume(1 :: "asd" :: 3 :: HNil)
res0: Seq[String] = List(1-1-1, a-s-d, 3-3-3)

Used like so:

CREATE OR REPLACE FUNCTION DateAdd(diffType varchar(15), incrementValue int, inputDate timestamp) RETURNS timestamp AS $$
DECLARE
   YEAR_CONST Char(15) := 'year';
   MONTH_CONST Char(15) := 'month';
   WEEK_CONST Char(15) := 'week';
   DAY_CONST Char(15) := 'day';
   HOUR_CONST Char(15) := 'hour';

   dateTemp timestamp;
   intervals interval;
BEGIN
    IF lower($1) = lower(YEAR_CONST) THEN
        select cast(cast(incrementvalue as character varying) || ' year' as interval) into intervals;
    ELSEIF lower($1) = lower(MONTH_CONST) THEN
        select cast(cast(incrementvalue as character varying) || ' months' as interval) into intervals;
    ELSEIF lower($1) = lower(DAY_CONST) THEN
        select cast(cast(incrementvalue as character varying) || ' day' as interval) into intervals;
    ELSEIF lower($1) = lower(WEEK_CONST) THEN
        select cast(cast(incrementvalue as character varying) || ' week' as interval) into intervals;
    ELSEIF lower($1) = lower(HOUR_CONST) THEN
        select cast(cast(incrementvalue as character varying) || ' hour' as interval) into intervals;
    END IF;

   dateTemp := inputdate + intervals;

   RETURN dateTemp;
END;
$$ LANGUAGE plpgsql;

It supports adding years, months, weeks, days, hours. More support could be added

Postgres INTERVAL使用表中的值

3 个答案: