sql - 选择查询问题

Question

我在 mysql 数据库中有一个表，其中包含字段

“名称”、“标题”、“cd_id”、“轨道”

条目如下所示:

Schubert | Symphonie Nr 7 | 27 | 2Brahms | Symphonie Nr 1 | 11 | 4Brahms | Symphonie Nr 2 | 27 | 4Shostakovich | Jazz Suite Nr 1 | 19 | 3

To get the tracks per cd (cd_id) I have written this script:

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

my $dbh = DBI->connect( 
    "DBI:mysql:database=my_db;", 
    'user', 'passwd', { RaiseError => 1 } );

my $select_query = "SELECT cd_id, tracks FROM my_table";

my $sth = $dbh->prepare( $select_query );
$sth->execute;

my %hash;
while ( my $row = $sth->fetchrow_hashref ) {
    $hash{"$row->{cd_id}"} += $row->{tracks};
}

print "$_ : $hash{$_}\n" for sort { $a <=> $b } keys %hash;

是否可以通过适当的选择查询直接获取这些结果？

Answer 1

"SELECT cd_id, SUM(tracks) as tracks FROM my_table GROUP BY cd_id"

编辑:请参阅此处了解更多信息以及您可以使用 GROUP BY 执行的其他操作:http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html