Amazon Interview Question for Software Engineer / Developers

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Prepared statements are a capability whereby the SQL queries are compiled into a intermediate form. The server then hands the client a handle for these. After this the only thing that remains to be parsed on query execution are the parameter values. For example if you had a query
select * from Foo where col=?
Where value of col depends upon (say) a user input. If you use prepared statements then the only thing that needs to be parsed by the server before query execution is the value of col. OTOH if you used regular queries the server would need to parse the incoming SQL (select * from ...) as well.
The second advantage of this security. If you send raw user input to the server I can try tricks like entering "10; drop table Users" in the dialog that you are getting the input from. So your final query would become
select * from Foo where col=1; drop table Users;
Now assuming you had a table called Users, I have just deleted that table. This is called SQL injection. With prepared statements this problem simply goes away.

Finally, indexing (in a DB context) is a way of optimizing look up of certain column (or sequence of columns) in a table. The database engine, then creates structures to quickly search for these columns, without requiring to scan the entire table.

- Jasmeet bagga May 12, 2010 | Flag Reply

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