关于postgresql：从连接日期和时间列获取时间戳


Get a timestamp from concatenating day and time columns

我在数据库中有日期和时间字段。 我希望通过连接日期和时间来获得时间戳。 如何在PostgreSQL中执行此操作？

我这样做了：

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SELECT EXTRACT(EPOCH FROM TIMESTAMP '2011-05-17 10:40:28');

它工作正常。

但是当我尝试替换日期和时间字段时，我收到以下错误：

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SELECT EXTRACT(EPOCH FROM TIMESTAMP DAY || ' ' || TIME);
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2
ERROR:  syntax error at OR near"Day"
LINE 1: ...quest_count > 0 AND (EXTRACT(EPOCH FROM TIMESTAMP DAY || ' ' || TIME)) > (e...
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date和time类型

如果Day的类型为date且time的类型为time，则有一个非常简单的解决方案：

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SELECT EXTRACT(EPOCH FROM (DAY + TIME));

您只需添加date和time即可获得timestamp [without time zone](根据会话的时区设置进行解释)。

而且，严格来说，提取时代本身与您的问题无关。
date + time会产生timestamp，就是这样。

字符串类型

如果您正在讨论字符串文字或text / varchar列，请使用：

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SELECT EXTRACT(EPOCH FROM ('2013-07-18' || ' ' || '21:52:12')::TIMESTAMP);

要么

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SELECT EXTRACT(EPOCH FROM CAST('2013-07-18' ||' '|| '21:52:12' AS TIMESTAMP));

你的表格不起作用

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<strike>SELECT EXTRACT(EPOCH FROM TIMESTAMP ('2013-07-18' || ' ' || '21:52:12'));</strike>

这可行：

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SELECT EXTRACT(EPOCH FROM"timestamp" ('2013-07-18' || ' ' || '21:52:12'));

我引用关于类型转换的手册：

It is also possible to specify a type cast using a function-like
syntax:

typename ( expression )

However, this only works for types whose names are also valid as
function names. For example, double precision cannot be used this way,
but the equivalent float8 can. Also, the names interval, time, and
timestamp can only be used in this fashion if they are double-quoted,
because of syntactic conflicts. Therefore, the use of the
function-like cast syntax leads to inconsistencies and should probably
be avoided.

大胆强调我的。
它的要点：而是使用前两种语法变体之一。

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SELECT EXTRACT(EPOCH FROM (DAY || ' ' || TIME)::TIMESTAMP);
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