How can I optimize my query (rank query)?

Question

For the last two days, I have been asking questions on rank queries in Mysql. So far, I have working queries for

1. query all the rows from a table and order by their rank.
2. query ONLY one row with its rank

Here is a link for my question from last night

How to get a row rank?

As you might notice, btilly's query is pretty fast.

Here is a query for getting ONLY one row with its rank that I made based on btilly's query.

set @points = -1; 
set @num = 0;

select * from (

SELECT id
  , points
  , @num := if(@points = points, @num, @num + 1) as point_rank
  , @points := points as dummy
FROM points
ORDER BY points desc, id asc

) as test where test.id = 3

the above query is using subquery..so..I am worrying about the performance.

are there any other faster queries that I can use?

Table points

id      points
1   50
2   50
3   40
4   30
5   30
6   20

Answer 1

Don't get into a panic about subqueries. Subqueries aren't always slow - only in some situations. The problem with your query is that it requires a full scan.

Here's an alternative that should be faster:

SELECT COUNT(DISTINCT points) + 1
FROM points
WHERE points > (SELECT points FROM points WHERE id = 3)

Add an index on id (I'm guessing that you probably you want a primary key here) and another index on points to make this query perform efficiently.