API functions

1. prepare() function
 The SQL "SELECT" statement is done by using the API prepare() function.
 The result is stored in the key word  $sth (Statement handle object). 
 
 
2. execute() function
 A statement is executed by using the API function execute(). 
 
 
3. finish() function
 The Stattement handle is released by the API function finish(). 
 
 
4. fetchrow_array() function
 The API function  fetchrow_array()  fetches all the results one by one 
 and printing those results.

 
5. commit function
 $dbh->commit or die $dbh->errstr;
We finalize an operation by the commit  function when everything 
goes fine. No changes are possible after this operation.

 
6. frollback function
If we want to revert back the changes made, we use rollback API 
operation:
$dbh->rollback or die $dbh->errstr;

7. AutoCommit function
This option can be used to avoid write commit function 
each time we want a query to be accomplished. Instead of 
issuing a lot of commits, we then set one time "Autocommit" 
after a connection call.

my $dbh = DBI->connect($dsn, $userid, $password,
              {AutoCommit => 1}) 
              or die $DBI::errstr;
AutoCommit can take value 0 or 1.

8. begin_work API function
begin_work API function turns AutoCommit off until the next call 
to commit or rollback that will turn AutoCommit on again.
$rc  = $dbh->begin_work   or die $dbh->errstr;

9. "do" function
Sometimes, there is no outputs from an operation. For 
example If we are doing an UPDATE, INSERT, or DELETE. We 
can just use "do" statement to execute a command. For example 
the command:
$dbh->do('DROP TABLE table name');
returns a true value if it succeeded, and a false value if 
it failed. In the case it succeeds it returns the number of 
affected rows. 

10. RaiseErrors function
The API RaiseErrors option handles errors automatically when we make 
a connection. This option is convenient when we want 
to abort a program instead of returning a failure code if 
an arror occurs.

my $dbh = DBI->connect($dsn, $userid, $password,
              {RaiseError => 1})
              or die $DBI::errstr;
RaiseError takes value 0 or 1.

11. Disconnecting Database
To disconnect Database connection, we use the disconnect API 
function "disonnect".
$rc = $dbh->disconnect  or warn $dbh->errstr;
Once it is issued, some  Database systems commit changes 
automatically, whereas others rollback any changes. When AutoCommit 
is not used, it is safe to call commit or rollback before calling 
disconnect.