sql show partition based on calculated column with mysql

问题

Let's pretend we have this relation:

╔═══════════════════╗
║ i++ name  score   ║
╠═══════════════════╣
║ 1   Will  123     ║
║ 2   Joe   100     ║
║ 3   Bill  99      ║
║ 4   Max   89      ║
║ 5   Jan   43      ║
║ 6   Susi  42      ║
║ 7   Chris 11      ║
║ 8   Noa   9       ║
║ 9   Sisi  4       ║
╚═══════════════════╝

Now I need a subset based on the data I am searching for. For instance I'm searching for the fith place. In my result I need more than the record of Jan, I need the two records before Jan and the two records behind Jan too. So I have the following resultset:

╔═══════════════════╗
║ id++ name score   ║
╠═══════════════════╣
║ 3   Bill  99      ║
║ 4   Max   89      ║
║ 5   Jan   43      ║
║ 6   Susi  42      ║
║ 7   Chris 11      ║
╚═══════════════════╝

That is the sql I got:

select @a:= id from quiz.score where username = 'Jan'; 
set @i=0;
SELECT @i:=@i+1 as Platz, s.* 
FROM quiz.score s where id BETWEEN @a-5 AND @a+5 
order by points desc;

The problem here is that @a is the id of the record. Is there a way to use the calculated value @i:=@i+1?

Thx a lot for your help.

回答1:

If you do not need the rank in your output (and it appears from your comments and favored answers that you do not), you can simply combine the quiz scores nearest to Jan's score:

Query (SQL Fiddle here):

-- XXX this assumes `scores`.`username` is UNIQUE !
SELECT * FROM (
    -- Get those who scored worse (or tied)
    (    SELECT s.*
           FROM scores s
     CROSS JOIN (SELECT score FROM scores WHERE username = 'Jan') ref
          WHERE s.score <= ref.score AND username <> 'Jan'
       ORDER BY s.score DESC
          LIMIT 2)
    UNION
    -- Get our reference point record
    (SELECT s.* FROM scores s WHERE username = 'Jan')
    UNION
    -- Get those who scored better
    (    SELECT s.*
           FROM scores s
     CROSS JOIN (SELECT score FROM scores WHERE username = 'Jan') ref
          WHERE s.score > ref.score AND username <> 'Jan'
       ORDER BY s.score ASC
          LIMIT 2)
) slice
ORDER BY score ASC;

(Note that I LIMITed the results to two records before Jan and two after Jan because your sample data set was so small.)

Those parentheses on the constituent queries above are needed to allow LIMIT and UNION to work together. The outermost query then lets us ORDER the results of a UNION.

回答2:

It's not entirely clear what you want, but a creative use of limit might be able to help:

Set @i = 0;

Select
  (@i := @i + 1) + 2 place,
  s.*
From
  quiz_score s
Order By
  quality Desc
Limit 
  2, 5;

Example Fiddle

回答3:

I have a working solution for you. The main point was to increment variable in WHERE clause.

The below code displays 7 rows: 3 below 'Jan', 'Jan' itself, and 3 after.

SET @i=0;

SELECT @n:=id, @s:=points FROM Score c WHERE c.username='Jan' ORDER BY points DESC;
SELECT (@i:=@i+1) FROM Score c WHERE c.id <> @n AND c.points <= @s;
SELECT (@i:=@i+1) FROM Dual;

SET @k=0;

SELECT s.* FROM Score s WHERE (@k:=@k+1) >= @i-3 AND @k<= @i+3  ORDER BY points DESC;

SQL Fiddle

Let me know if any clarifications are required.

来源：https://stackoverflow.com/questions/19211700/sql-show-partition-based-on-calculated-column-with-mysql

标签

mysql

sql

ranking