Perl 如何将postgres dbd占位符用于DB对象名称

（或者如何使用perl DBI（DBD:：PG）和占位符迭代信息模式？）

Windows7、ActiveState Perl 5.20.2、PostgreSQL 9.4.1

下面的案例A、B和C在使用占位符作为列值时成功。为了

• 没有使用占位符

• 传递一个文本

• 传递了一个变量（用相同的文本填充）

将其提升到DB对象级别将是非常好的。。（表格、视图等）

下面是案例D的错误输出：

Z:\CTAM\data_threat_mapping\DB Stats\perl scripts>test_placeholder.pl

A Row Count: 1
B Row Count: 1
C Row Count: 1

DBD::Pg::st execute failed: ERROR:  syntax error at or near "$1"

LINE 1: SELECT COUNT(*) FROM $1 WHERE status = 'Draft';
                             ^ at Z:\CTAM\data_threat_mapping\DB     Stats\perl 
scripts\test_placeholder.pl line 34.

多谢指点

#!/usr/bin/perl -w
use strict;
use diagnostics;
use DBI;

my $num_rows = 0;

# connect
my $dbh = DBI->connect("DBI:Pg:dbname=CTAM;host=localhost",
                       "postgres", "xxxxx",
                       { 'RaiseError' => 1, pg_server_prepare => 1 });

#---------------------
# A - success
my $sthA = $dbh->prepare(
    "SELECT COUNT(*) FROM cwe_compound_element WHERE status = 'Draft';"
);
$sthA->execute(); # no placeholders

#---------------------
# B -  success
my $sthB = $dbh->prepare (
    "SELECT COUNT(*) FROM cwe_compound_element WHERE status = ?;"
);
$sthB->execute('Draft'); # pass 'Draft' to placeholder

#---------------------
# C -  success
my $status_value = 'Draft';
my $sthC = $dbh->prepare(
    "SELECT COUNT(*) FROM cwe_compound_element WHERE status = ?;"
);
$sthC->execute($status_value); # pass variable (column value) to placeholder

#---------------------
# D - failure
my $sthD = $dbh->prepare(
    "SELECT COUNT(*) FROM ? WHERE status = 'Draft';"
);
$sthD->execute('cwe_compound_element'); # pass tablename to placeholder

我试过单引号/双引号/无引号（q，qq）.

如果

SELECT * FROM Foo WHERE field = ?

意味着

SELECT * FROM Foo WHERE field = 'val'

然后

意味着

这显然是错误的。占位符只能在表达式中使用。修正：

my $sthD = $dbh->prepare("
   SELECT COUNT(*)
    FROM ".$dbh->quote_identifier($table)."
   WHERE status = 'Draft'
");
$sthD->execute();

如果

意味着

SELECT * FROM Foo WHERE field = 'val'

然后

意味着

这显然是错误的。占位符只能在表达式中使用。修正：

my $sthD = $dbh->prepare("
   SELECT COUNT(*)
    FROM ".$dbh->quote_identifier($table)."
   WHERE status = 'Draft'
");
$sthD->execute();