将列表传递给where子句 [英] passing a list to a where clause

问题描述

我正在尝试从SQL导出到.csv，如果我对其进行硬编码以接受一定数量的参数，则它可以工作。问题是，我想允许用户请求任意数量的参数，并将它们传递给where子句。代码应该使它更清晰。

I am trying to export from SQL to .csv and it works if I hard code it to accept a certain number of arguments. The things is, I want to allow the user to request any number of arguments and have these be passed to the where clause. The code should make this a bit more clear.

create temporary table bdates as

 select tt.date, tt.time, tt.location
 from birthdays as bd
 inner join days as d
   on (d.id = bd.birth_id)
 inner join total_time as tt
   on (bd.date = tt.date and
       bd.time = tt.time and
       d.day_of = tt.location)
 where tt.date in(:date1, :date2) --defined by user at command line
 order by...

\copy bdates to '.csv'

所以我想我要做的是将列表传递给where子句，而不是显式的：dates＃变量。例如，一个人可以使用参数 2012-01-04 12：00、2012-02-04 12：00、2012-03-04 12:00或两个或一个参数来运行脚本。对于三个字符串，该字符串将解析为 2012-01-04 12:00， 2012-02-04 12:00， 2012-03-04 12:00。

So what I think I want to do is pass a list to that where clause instead of explicit :dates# variables. For example, a person could run the script with the argument '2012-01-04 12:00, 2012-02-04 12:00, 2012-03-04 12:00', or just two arguments or one. In the case of three the string would be parsed to '2012-01-04 12:00', '2012-02-04 12:00', '2012-03-04 12:00'.

我已经尝试过string_to_array（），unnest（regexp_matches（：dates，expression））和regexp_split_to_table（：dates，expression），尽管我不确定如何进行连接。我尝试过的各种解决方案都产生了许多错误，包括：

I've tried string_to_array(), unnest(regexp_matches(:dates, expression)) and regexp_split_to_table(:dates, expression), though I'm not sure how to do the join. the various solutions I've tried have produced numerous errors including:

无法将类型text []转换为没有时区的时间戳

cannot cast type text[] to timestamp without time zone

无法将类型记录转换为没有时区的时间戳

cannot cast type record to timestamp without time zone

regexp_split不支持全局选项

regexp_split does not support the global option

WHERE的参数不能返回一个集合

argument of WHERE must not return a set

最后一个特别令人沮丧，我很茫然，不胜感激。有一种更简单的方法，不是吗？谢谢！

The last one is especially disheartening and I'm at a loss and would appreciate any input. There's a simpler way to do this, isn't there? Thanks!

推荐答案

尝试一下：

create table x(d timestamp);

insert into x values
('jan 2, 2012'),
('february 4, 2012 12:00'),
('jan 4, 2012 12:00'),
('march 1, 2012'),
('may 3, 2012');

查询：

with input as
(
  select 
  '2012-1-2, 2012-01-04 12:00, 2012-02-04 12:00, 2012-03-04 12:00'::text
  as d_input
)
,converted_to_array as
(
  select ('{' || d_input || '}')::timestamp[] as d_array
  from input 
)
select d
from x cross join converted_to_array
where d = any(d_array)

输出：

D
January, 02 2012 00:00:00-0800
February, 04 2012 12:00:00-0800
January, 04 2012 12:00:00-0800

实时测试： http://www.sqlfiddle.com/#!1/43d48/26

您也可以使用IN，只是将数组嵌套到行：

You can also use IN, just unnest array to rows:

with input as
(
  select 
  '2012-1-2, 2012-01-04 12:00, 2012-02-04 12:00, 2012-03-04 12:00'::text
  as d_input
)
,converted_to_array as
(
  select ('{' || d_input || '}')::timestamp[] as d_array
  from input 
)
select d
from x cross join converted_to_array
where d in (select unnest(d_array))

实时测试： http://www.sqlfiddle.com/#!1/43d48/29

您也可以将它们全部放在一行中：

You can put them all in one line too:

select d
from x 
where d in (select unnest( ('{' || '2012-1-2, 2012-01-04 12:00, 2012-02-04 12:00, 2012-03-04 12:00'::text || '}')::timestamp[] ))

但是我犹豫不决，因为这会在stackoverflow上引起水平滚动条：-）

But I hesitates to do so, as it causes horizontal scrollbar here on stackoverflow :-)

实时测试： http://www.sqlfiddle.com/#!1/43d48/31

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