Question

Running the following query

SET @rownum := 0;    
SELECT customer_id, @rownum := @rownum +1 AS rank, score
FROM game_table_customers gtc
INNER JOIN customers c ON c.customers_id = gtc.customer_id
INNER JOIN game_table gt ON gtc.table_id = gt.table_id
WHERE c.my_team =11095
AND gt.event_id =21110
ORDER BY score DESC
LIMIT 0 , 30

The correct result should look like this

CustID  Rank    Score
2        1     130000
39       2     99426
84       3     99178
259      4     98963
339      5     97796

However, what I am getting is the following

CustID  Rank    Score
2        2      130000
39      11      99426
84      20      99178
259     54      98963
339     69  97796

When I exclude the event_id clause I get the correct result. However when the event_id is included it skews it. I have tried only the event_id (removing the my_team clause) and same incorrect result.

Any ideas/suggestions as to why the result may be off would be much appreciated

Answer 1

I guess this has to do with the execution plan selected in every case and the mix with applying of row numbers – in some of those plans. The row numbers are calculated and then the WHERE conditions are evaluated, so you see non-consecutive row numbers.

Try this (first getting the 30 results you need, then applying row numbers):

SET @rownum := 0; 
SELECT customer_id, @rownum := @rownum +1 AS rank, score
FROM
  ( SELECT customer_id, score
    FROM game_table_customers gtc
      INNER JOIN customers c ON c.customers_id = gtc.customer_id
      INNER JOIN game_table gt ON gtc.table_id = gt.table_id
    WHERE c.my_team =11095
      AND gt.event_id =21110
    ORDER BY score DESC
    LIMIT 0 , 30
  ) tmp
ORDER BY score DESC

---

I can’t test it now but you can also try this:

SELECT customer_id, @rownum := @rownum +1 AS rank, score
FROM game_table_customers gtc
  INNER JOIN customers c ON c.customers_id = gtc.customer_id
  INNER JOIN game_table gt ON gtc.table_id = gt.table_id
  CROSS JOIN (SELECT @rownum := 0 AS rn) dummy  
WHERE c.my_team =11095
  AND gt.event_id =21110
ORDER BY score DESC
LIMIT 0 , 30