Re^2: Quickest way of fetching a Single row and column in MySQL using DBI

[cees]

Although your version works, it is potentially open to an SQL injection attack through the $username variable. With DBI that is easy to avoid by using placeholders. Also, I think you want selectrow_array (selectrow_arrayref returns a reference to an array, wheras selectrow_array will return a list, or just a scalar value if you are selecting a single column).

my $id = $dbh->selectrow_array("SELECT id FROM users where username = 
+?", {}, $username);

[perrin]

I think you need array context there:

my ($id) = $dbh->selectrow_array("SELECT id FROM users where username 
+= ?", {}, $username);

[cees]

Scalar context works as well according to the DBI source code:

sub selectrow_array {
  my $row = _do_selectrow('fetchrow_arrayref', @_) or return;
  return $row->[0] unless wantarray;
  return @$row;
}

The docs hint that this should work as well, but don't explicitly state it. Instead the docs mention this:

If called in a scalar context for a statement handle that has more than one column, it is undefined whether the driver will return the value of the first column or the last. So don't do that.

Anyway, it won't hurt to add the brackets in there to force list context, but it shouldn't be required.

[jZed]

Quoting the DBI docs is insufficient because the DBDs can override this. Forcing array context is not required because only a single column is being fetched regardless of which DBD is in use. Whenever more than one column is being fetched you should force list context if you care at all about portability. In scalar context, some DBDs return the first of the multiple columns and some return the last. Personally I try to always force the list context since it doesn't ever hurt and it sometimes helps.