Question

I’m using the following SQL statement:

SELECT
  SUM(t.Points) AS `Points`,
  CONCAT(s.Firstname, " ", s.Surname) AS `Name`
FROM transactions t
INNER JOIN student s
  ON t.Recipient_ID = s.Frog_ID
GROUP BY t.Recipient_ID

The query takes 21 seconds to run. Bizarrely, even if I LIMIT 0, 30 it still takes 20.7 seconds to run!

If I run an EXPLAIN on this statement, the results are as follows:

id  select_type table   type    possible_keys   key     key_len     ref     rows        Extra
1   SIMPLE      s       ALL     PRIMARY         NULL    NULL        NULL    877         Using temporary; Using filesort
1   SIMPLE      t       ALL     NULL            NULL    NULL        NULL    135140      Using where

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A transaction takes the following form:

Transaction_ID  Datetime    Giver_ID    Recipient_ID    Points  Category_ID     Reason
1               2011-09-07  36754       34401           5       6               Gave excellent feedback on the new student noteboo...

There are 130,000 rows in the transactions table.

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A student takes the following form:

Frog_ID UPN             Firstname   Surname     Intake_Year
101234  K929221234567   Madeup      Student     2010

There are 835 rows in the student table.

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Indexes

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Is there a way I can make this query more efficient?

Answer 1

You both join using Recepient_ID and group by it, yet it’s not indexed, so I assume this is the problem.

Try to add transactions.Recepient_ID as an index.