[英]PL/PGSQL function - passing a TEXT argument to date_trunc()
我想创建一个返回历史日期的简单实用程序函数。
这是我写的函数:
CREATE FUNCTION testdate(duration TEXT) RETURNS DATE AS $$
BEGIN
SELECT * FROM date_trunc('day', NOW() - interval duration);
END
$$ LANGUAGE plpgsql;
当我尝试创建函数时,出现以下错误:
ERROR: syntax error at or near "duration"
LINE 3: SELECT * FROM date_trunc('day', NOW() - interval duration);
^
当我删除interval
关键字时,我可以创建该函数,但是当我尝试如下使用它时:
SELECT * from testdate('1 month');
我收到以下错误消息:
ERROR: operator does not exist: timestamp with time zone - text
LINE 1: SELECT * FROM date_trunc('day', NOW() - duration)
^
HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.
QUERY: SELECT * FROM date_trunc('day', NOW() - duration)
CONTEXT: PL/pgSQL function testdate(text) line 3 at SQL statement
如何正确将参数传递给date_trunc
?
我假设您尝试执行以下操作:
CREATE or replace FUNCTION testdate(duration interval) RETURNS DATE AS $$
BEGIN
return (SELECT * FROM date_trunc('day', NOW() - duration));
END
$$ LANGUAGE plpgsql;
用法:
select * from testdate('1 month');
testdate
------------
2017-12-23
(1 row)
当然可以:
CREATE or replace FUNCTION testdate(duration text) RETURNS DATE AS $$
BEGIN
return (SELECT * FROM date_trunc('day', NOW() - duration::interval));
END
$$ LANGUAGE plpgsql;
与文本参数,只是为了回答您的问题,但我想说的是适当的数据类型会更有意义...
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