Re: DBI determine primary key

Specifically for mysql, you can use a special SQL command: DESCRIBE $table. Yes that works in DBI too. Here's a test table "foo", which I put into the database "test" (present by default):

CREATE TABLE foo(
  id int(10) unsigned NOT NULL AUTO_INCREMENT,
  letter char(1) NOT NULL,
  name text NOT NULL,
  num float NULL,
  PRIMARY KEY (id)
);
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And here's some demo code checking what we've got:

#!/usr/local/bin/perl -w
use DBI;
my $dbh = DBI->connect('dbi:mysql:test', "", "", { PrintError => 0 , R
+aiseError => 1});
END { $dbh->disconnect if $dbh }
use Data::Dumper;

my $sth = $dbh->prepare('DESCRIBE foo');
$sth->execute;
while(my $r = $sth->fetchrow_hashref) {
    print Dumper $r;
}
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which shows:

$VAR1 = {
          'Extra' => 'auto_increment',
          'Field' => 'id',
          'Default' => undef,
          'Key' => 'PRI',
          'Type' => 'int(10) unsigned',
          'Null' => ''
        };
$VAR1 = {
          'Extra' => '',
          'Field' => 'letter',
          'Default' => '',
          'Key' => '',
          'Type' => 'char(1)',
          'Null' => ''
        };
$VAR1 = {
          'Extra' => '',
          'Field' => 'name',
          'Default' => '',
          'Key' => '',
          'Type' => 'text',
          'Null' => ''
        };
$VAR1 = {
          'Extra' => '',
          'Field' => 'num',
          'Default' => undef,
          'Key' => '',
          'Type' => 'float',
          'Null' => 'YES'
        };
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4 records, one for each field. 'Field' contains the field name. In particular, check out the contents of the field 'Key': its value is "PRI" for the primary key, the empty string for the rest.

Comment on Re: DBI determine primary key Select or Download Code

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Re: Re: DBI determine primary key by Anonymous Monk on Apr 09, 2004 at 02:37 UTC
Actually, a different way using a different SQL query (which I was hoping to avoid, since that's dependent on parsing specific output): `my $keys_ref = $dbh->selectall_arrayref("SHOW KEYS FROM $table"); + foreach my $row ( @{$keys_ref} ) { print "Primary key: $row->[4]" if $row->[2] eq 'PRIMARY'; }` [download] It'd probably be more readable to use a selectall_hashref and (in the MySQL case) snag `$row->{'Column_name'} if $row->{'Key_name'} eq 'PRIMARY'` [download] Edited by Chady -- added code tags.	[reply] [d/l] [select]

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Re: Re: DBI determine primary key
by Anonymous Monk on Apr 09, 2004 at 02:37 UTC

my $keys_ref = $dbh->selectall_arrayref("SHOW KEYS FROM $table");     
+             
    
foreach my $row ( @{$keys_ref} ) {
    print "Primary key: $row->[4]"
        if $row->[2] eq 'PRIMARY';
}
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$row->{'Column_name'} if $row->{'Key_name'} eq 'PRIMARY'
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Edited by Chady -- added code tags.

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