What does "foo" mean in this SQL Server Query ?

Question

for eg...

SELECT * 
  FROM ( SELECT RANK() OVER (ORDER BY stud_mark DESC) AS ranking,
                stud_id, 
                stud_name, 
                stud_mark 
           FROM tbl_student ) AS foo 
 WHERE ranking = 10

Here foo is present...actually what it does ?..

Answer 1

It's a table alias/identifier for the derived query

Without it, you'll get an error because the derived table has no identifier

SELECT * FROM 
 ( SELECT RANK() OVER (ORDER BY stud_mark DESC) AS ranking, stud_id, stud_name, stud_mark FROM tbl_student )
WHERE ranking = 10

Answer 2

It is just an alias.

Aliases help you reduce the amount of text you may have to type out when writing queries.

For instance this:

SELECT customer.Name, customer.OpenDate FROM customer

Can be shortened to:

SELECT c.Name, c.OpenDate FROM customer c

In your example, it is a derived table (not a physical one) which now you can actually say:

SELECT foo.someField rather then SELECT *

Answer 3

In this example, foo is a table alias. Here's how you'd use it:

SELECT foo.* 
  FROM ( SELECT RANK() OVER (ORDER BY ts.stud_mark DESC) AS ranking,
                ts.stud_id, 
                ts.stud_name, 
                ts.stud_mark 
           FROM tbl_student ts) AS foo 
 WHERE foo.ranking = 10

SQL Server (and MySQL for that matter) will throw an error if you do not specify a table alias for a derived table (AKA inline view).

Answer 4

It would be better to ask: What does the expresison after "AS" mean in SQL?

As Jon said, it's an alias. You can use it instead of the expression before the AS.

SELECT veryverylongname AS V FROM dummy_table AS D WHERE D.V = 10

Here you can see two aliases V for the field and D for the table.

You can also use it to alias complete SELECT-statements as in your example. The alias will then represent the table resulting from the sub-query, and will have the fields specifiy in the subquery after your SELECT-keyword.

Answer 5

foo is just a word developers frequently use when they want to give name to variable, method etc. in example code or sample code and it doesn't necessarily need to be foo. It can be anything.

So the answer is you can write many other things instead of foo.