[FIXED] There is garbage data in sql-query but it is still executing, although not affecting any results. Why?

Issue

I am using mysql server for sql.
Select * from products some_garbage_value; and

Select * from products;

resulting the same value. Why?

Entering anything at the place of some_garbage_value, still result the same query result.

I have created a form to enter query and that form is handled by a servlet and after creating a connection, i am resulting the query result on that servlet.

Is this bad thing for my form, if yes then tell me, How to get rid of this bug? Is this a bug? Can it be a case of SQL Injection?

Solution

In

Select * from products some_garbage_value;

The some_garbage_value is not garbage, it is an alias. Technically this means that for the scope of query, you have 'renamed' this occurrence of the products table to some_garbage_value. This can be very useful if you need to disambiguate between two occurrence of the same table (eg in self-join), or to make your query more readable/self-explanatory (or just shorter).

It is equivalent to

Select * from products as some_garbage_value;

See also the MySQL reference for select:

The FROM table_references clause indicates the table or tables from which to retrieve rows. If you name more than one table, you are performing a join. For information on join syntax, see Section 13.2.9.2, “JOIN Syntax”. For each table specified, you can optionally specify an alias.

tbl_name [[AS] alias] [index_hint]

This wouldn't work with just any value: it must be a syntactically valid identifier.

Answered By - Mark Rotteveel