Database Read Operation in Perl

Perl READ Operation on any databasse means to fetch some useful information from the database, i.e., one or more records from one or more tables. So once our database connection is established, we are ready to make a query into this database. Following is the procedure to query all the records having AGE greater than 20. This will take four steps −

• Preparing SQL SELECT query based on required conditions. This will be done using prepare() API.
• Executing SQL query to select all the results from the database. This will be done using execute() API.
• Fetching all the results one by one and printing those results.This will be done using fetchrow_array() API.
• Releasing Stattement handle. This will be done using finish() API.

my $sth = $dbh->prepare("SELECT FIRST_NAME, LAST_NAME FROM TEST_TABLE WHERE AGE > 20");
$sth->execute() or die $DBI::errstr;
print "Number of rows found :" + $sth->rows;
while (my @row = $sth->fetchrow_array()) {
   my ($first_name, $last_name ) = @row;
   print "First Name = $first_name, Last Name = $last_name\n";
}
$sth->finish();

Using Bind Values

There may be a case when condition is not given in advance. So you can use bind variables, which will take the required values at run time. Perl DBI modules makes use of a question mark in place of actual value and then the actual values are passed through execute() API at the run time. Following is the example −

$age = 20;
my $sth = $dbh->prepare("SELECT FIRST_NAME, LAST_NAME FROM TEST_TABLE WHERE AGE > ?");
$sth->execute( $age ) or die $DBI::errstr;
print "Number of rows found :" + $sth->rows;
while (my @row = $sth->fetchrow_array()) {
   my ($first_name, $last_name ) = @row;
   print "First Name = $first_name, Last Name = $last_name\n";
}
$sth->finish();