使用Perl

Question

我試圖運行使用PostgreSQL

use DBI; 

$database = "postgres"; 
$user  = "postgres"; 
$password = "admin"; 

my $dbh = DBI->connect( "dbi:Pg:dbname=$database" 
         , $user 
         , $password 
        ) 
or die "Can't Connect to database: $DBI::errstr\n"; 

# get data from the URL string 
my $firstname = "haroon"; 
my $lastname ="ash"; 
my $age = 24; 

# insert the data into the database 
my $query = "INSERT INTO people (firstname, lastname, age) 
      VALUES ('$firstname','$lastname', '$age')"; 
$dbh->do($query); 

# get the ID of the inserted person 
$query = "SELECT MAX(id) FROM people"; 
my $sth = $dbh->prepare($query); 
my $rv =$sth->execute; 
if($rv < 0){ 
    print $DBI::errstr; 
} 
else { 
    my $row = $sth->fetchrow_hashref; 
    my $person_id = $row->{'max'}; 
    print $firstname, $lastname 
     . "was successfully inserted at position " 
     . $person_id; 
} 

我想打印的我已經進入了最新的人物ID用Perl一個簡單的數據庫連接擷取來自數​​據庫的一個單列。但my $person_id = $row->{'max'}似乎給我正確的答案，而不是my $person_id = $row->{'id'};。我不明白這是爲什麼。

Answer 1

您可能需要設置查詢列別名，

$query = "SELECT MAX(id) AS id FROM people"; 

爲Postgres的是把自己的別名你，那就是max。

如果你想要的是最後插入的ID，你可以

my $query = "INSERT INTO people (firstname, lastname, age) 
     VALUES (?,?,?) 
     returning id 
"; 

，並獲取查詢，你會與select做。 （檢查pg docs）

Answer 2

您未在插入語句中輸入PERSON_ID。

相反，似乎ID字段由數據庫填充，插入期間自動增量值，似乎。

不知道表定義（和表上的潛在插入觸發器）很難/不可能給你一個更好的答案。

Answer 3

可以使用RETURNING關鍵字返回與您剛插入的行相關聯的id：

my $query = ' 
    INSERT INTO people (firstname, lastname, age) 
    VALUES ($1, $2, $3) 
    RETURNING id'; 
my $sth = $dbh->prepare($query); 
$sth->execute($firstname, $lastname, $age); 
my $rv = $sth->fetchrow_hashref(); 
printf "%s, %s was successfully inserted at position %d\n", 
    $firstname, $lastname, $rv->{id};