如何在带引号的占位符中使用查询？ （Perl / PostgreSQL） [英] How can I use a query with placeholder inside quotes? (perl / postgresql)

问题描述

我正在尝试执行以下脚本：

I'm trying to execute the following script:

#!/usr/bin/perl -w

use strict;
use DBI;

my $db = "Pg";
my $db_database = "whatever";
my $user = "whatever";
my $password = "whatever";

my $dbh = DBI->connect("dbi:$db:dbname=$db_database", $user, $password);

my $query = $dbh->prepare (q{SELECT
                   arrival_date - INTERVAL '? MINUTE'
                   FROM emails LIMIT 1})
  or die ("unable to prepare");
$query->execute(60) or die("unable to execute");

print $query->fetchrow_array, "\n";

（到达日期的格式为：带时区的时间戳记，缺省为CURRENT_TIMESTAMP，不为NULL）

(arrival_date has this format: timestamp with time zone NOT NULL default CURRENT_TIMESTAMP)

问题在于未检测到问号占位符，因为其内部单引号：

The problem is that the question mark placeholder is not detected because its inside single quotes:

DBD::Pg::st execute failed: called with 1 bind variables when 0 are needed 

如果我使用$ 1占位符qq {}，并尝试了$ dbh-> quote的一些变体，那会有所帮助。我该如何工作？

It does not help if I use qq{}, $1 placeholder, and tried a few variations with $dbh->quote. How can I make this work?

推荐答案

您不能在引号内使用占位符。您可以使用SQL字符串连接，但是在这种情况下，使用乘法更容易做到：

You can't use placeholders inside quotes. You can use SQL string concatenation, but in this case, it's easier to do it by using multiplication:

my $query = $dbh->prepare (q{SELECT
                   arrival_date - ? * INTERVAL '1 MINUTE'
                   FROM emails LIMIT 1});
$query->execute(60);

这样，您不必附加'分钟'改为执行查询时的数字。

That way, you don't have to append ' minutes' to the number when you execute the query.

这篇关于如何在带引号的占位符中使用查询？ （Perl / PostgreSQL）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！