一个数据库应用程序，常常需要提供数据输入功能，即让用户输入数据，并存入数据库中，这就涉及到一个数据输入是否合法的问题。若用PowerBuilder来编写这种程序，实现这一点是非常方便的，因为PowerBuilder中每一个数据输入控件都可以单独对其输入进行控制，但Delphi没有提供这样的功能。我们用Delphi编写这样的程序时，就需要自己编写一些代码来实现。下面举一个很常见的例子加以说明。

-A database application, and often need to provide data input function, which allows users to input data, and deposited in the database, which relates to the legality of a data entry problem. If using PowerBuilder to write such a procedure, to achieve this is very convenient, because PowerBuilder data input of each control input can be its own control, but Delphi did not provide this function. We use Delphi to prepare such a program, will need to have written some code to achieve. The following is common to cite an example.