Question

#!/usr/bin/env perl
use warnings;
use strict;
use DBI;

my $dbh = DBI->connect( "DBI:CSV:", '', '', { RaiseError => 1 } ) or die DBI->errstr;

my $table = 'my_test_table_1.csv';
$dbh->do( "CREATE TEMP TABLE $table( id INTEGER, name CHAR(64) )" );

my $sth = $dbh->prepare( "INSERT INTO $table ( id, name ) VALUES( ?, ? )" );
$sth->execute( 1, 'Ruth' );
$sth->execute( 2, 'John' );
$sth->execute( 3, 'Nena' );
$sth->execute( 4, 'Mark' );

$sth = $dbh->prepare( "SELECT * FROM $table WHERE id > ? LIMIT ?" );
$sth->execute( 1, 2 );
$sth->dump_results;

# Bad limit clause! at /usr/local/lib/perl5/site_perl/5.20.1/SQL/Statement.pm line 88.

看起来LIMIT子句中的占位符不起作用。

当我使用DBD::CSV驱动程序时，如何判断SQL语句中某个位置是否支持占位符？

Answer 1

占位符只能在需要表达式的地方使用。 LIMIT后面的内容必须是行计数（不是表达式），因此它不能是占位符。

#!/usr/bin/perl
use warnings;
use strict;
use DBI qw( );

my $dbh = DBI->connect("DBI:CSV:", undef, undef, {
   PrintError => 0, RaiseError => 1,
} );

{
   my $sth = $dbh->prepare( "SELECT 1 LIMIT 1" );
   $sth->execute();
   $sth->finish();
   print "ok\n";
}

{
   my $sth = $dbh->prepare( "SELECT 1 LIMIT 0+1" );
   $sth->execute();
   $sth->finish();
   print "ok\n";
}

ok
DBD::CSV::db prepare failed: Bad limit clause! at .../SQL/Statement.pm line 88.
 [for Statement "SELECT 1 LIMIT 0+1"] at a.pl line 18.

Answer 2

根据documentation，占位符只能用于值。

DBD :: CSV和占位符

2 个答案: