$dbh = dbi -> connnect('DBI:Oracle:payroll') #This will use connect function from dbi this is like dbi.connect() in java
now we create a new perl variable $sth = $dbh -> prepare('SELECT * FROM people WHERE lastname = ?') # this is equivalent to $dbh.prepare()
but $dbh is not dbi, which has prepare(). Its string as a result of dbi -> connnect('DBI:Oracle:payroll').
shall it not be $sth = dbi -> prepare('SELECT * FROM people WHERE lastname = ?')