Before I give some alternative methods, I thought you might like to get the official explanation on the "rows" method - this is 'perldoc DBI' section on "rows":
"rows"
$rv = $sth->rows;
Returns the number of rows affected by the last row affecti
+ng com-
mand, or -1 if the number of rows is not known or not avail
+able.
Generally, you can only rely on a row count after a non-"SE
+LECT"
"execute" (for some specific operations like "UPDATE" and
"DELETE"), or after fetching all the rows of a "SELECT" sta
+tement.
For "SELECT" statements, it is generally not possible to kn
+ow how
many rows will be returned except by fetching them all. So
+me
drivers will return the number of rows the application has
+fetched
so far, but others may return -1 until all rows have been f
+etched.
So use of the "rows" method or $DBI::rows with "SELECT" sta
+tements
is not recommended.
One alternative method to get a row count for a "SELECT" is
+ to exe-
cute a "SELECT COUNT(*) FROM ..." SQL statement with the sa
+me "..."
as your query and then fetch the row count from that.
As the perldocs suggest, here's an example of doing a SELECT COUNT to get the number of rows found:
my $sql = {
SELECT count(*)
FROM patient_data
WHERE name = ?
};
my $sth = $dbh->prepare($sql);
$sth->execute($name);
my ($count_rows) = $sth->fetchrow_array();
or, you could fetch all the rows, one-by-one, and count them as you go, like:
my $sql = {
SELECT name
FROM patient_data
WHERE name = ?
};
my $sth = $dbh->prepare($sql);
$sth->execute($name);
my $count_rows = 0;
while (my ($name) = $sth->fetchrow_array()) {
### do something with $name here ###
$count_rows += 1;
}
Of course, I haven't done anything with error trapping the DBI statements here, but you definitely should.
HTH. |