How does Binding parameters prevent Sql Injection? [duplicate]

Question

In PHP, I've found a few methods to prevent Sql Injection. Binding parameters is one of them. But I'm unable to find a complete explanation of how binding parameters actually prevent Sql Injection. I was of the notion that binding parameters simply save time in binding different data to the same Sql statement. How does prevention of Sql injection come into picture?

Answer 1

I think a simple example will explain you the thing:

  "select * from myTable where name = " + condition;

imagine that user input as a condition is

  '123'; delete from myTable; commit;

what happens then? the query executed will be

  select * from myTable where name = '123'; delete from myTable; commit;

or actually we have three queries with disastrous consequences:

  select * from myTable where name = '123';
  
  delete from myTable; 
  
  commit;

in case of bind variables

  "select * from myTable where name = @prmName"

whatever user input is it'll be one and only one query and the weird input above will always be treated as a string, not as a part of query. The outcome will be (most probably) an empty cursor, since there're no names within myTable like

  "'123'; delete from myTable; commit;"