如何从 DBD::CSV 获取列名？
如何从表中获取column-names？这不起作用：
#!/usr/bin/env perl
use warnings;
use 5.012;
use DBI;
my $options = { RaiseError => 1, PrintError => 0, f_ext => ".csv/r" };
my $dbh = DBI->connect( "dbi:CSV:", undef, undef, $options ) or die $DBI::errstr;
my $table = 'test';
$dbh->do( "CREATE TEMP TABLE $table ( id INT, size INT )" );
my $sth = $dbh->prepare( "INSERT INTO $table ( id, size ) VALUES( ?, ? )" );
$sth->execute( 1, 235 );
$sth->execute( 2, 42 );
use Data::Dumper;
say Dumper $dbh->{csv_tables}{$table}{col_names};
$dbh->{csv_tables}{$table} = { skip_first_row => 0 };
$sth = $dbh->prepare( "SELECT * FROM $table" );
$sth->execute;
my @first_row = $sth->fetchrow_array;
say "@first_row\n";
$sth = $dbh->column_info( '', '', $table, '' );
my $ref = $sth->fetchall_arrayref;
say "@$_" for @$ref;
错误：
$VAR1 = undef;
1 235
Can't call method "fetchall_arrayref" on an undefined value at ./so.pl line 25.
How can I get the column-names from the table? This did not work:
#!/usr/bin/env perl
use warnings;
use 5.012;
use DBI;
my $options = { RaiseError => 1, PrintError => 0, f_ext => ".csv/r" };
my $dbh = DBI->connect( "dbi:CSV:", undef, undef, $options ) or die $DBI::errstr;
my $table = 'test';
$dbh->do( "CREATE TEMP TABLE $table ( id INT, size INT )" );
my $sth = $dbh->prepare( "INSERT INTO $table ( id, size ) VALUES( ?, ? )" );
$sth->execute( 1, 235 );
$sth->execute( 2, 42 );
use Data::Dumper;
say Dumper $dbh->{csv_tables}{$table}{col_names};
$dbh->{csv_tables}{$table} = { skip_first_row => 0 };
$sth = $dbh->prepare( "SELECT * FROM $table" );
$sth->execute;
my @first_row = $sth->fetchrow_array;
say "@first_row\n";
$sth = $dbh->column_info( '', '', $table, '' );
my $ref = $sth->fetchall_arrayref;
say "@$_" for @$ref;
Error:
$VAR1 = undef;
1 235
Can't call method "fetchall_arrayref" on an undefined value at ./so.pl line 25.
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column_info方法应该由驱动程序实现，如果尚未实现，您将得到undef。相反，我会在执行第一个查询后查看
$sth->{NAME}。顺便说一句，
DBD::CSV是一个有趣的玩具，但如果您需要一个轻量级的一次性数据库，我强烈建议使用DBD::SQLite。如果您只需要处理 CSV 数据，有几个不错的模块可以为您提供原始访问权限。在这两者之间，DBD::CSV有意义的用例非常少。The
column_infomethod is supposed to be implemented by the driver, and you getundefif it has not been.Instead I'd look at
$sth->{NAME}after you executed the first query.Incidentally
DBD::CSVis a fun toy, but if you need a lightweight throwaway database I strongly recommend usingDBD::SQLiteinstead. And if you just need to handle CSV data, there are several decent modules out there that give you raw access. Between those two, there are very few use cases left whereDBD::CSVmakes much sense.