MySQL中的简单评级系统

Question

Let's say I am running a small vote counter product. The values are stored in the database "content", with a row containing the amount of votes ("count"), I also have a row called "rank", how would I autosum these values so that I don't have to iterate through every single one in PHP, causing the script to slow down tremendously?

Answer 1

If you have a structure like this in a table

item with fields: name, id, count, ...

you can simply do:

Up vote in the item with id = $id

UPDATE item SET count = count + 1 WHERE id='$id';

Down vote in the item with id = $id

UPDATE item SET count = count - 1 WHERE id='$id';

count will store the total number of votes.

If you want to check for avoiding more than one vote per user/ip you should store each individual vote in another table and check this aditional table for non repeated votes before sending the previous queries.

Answer 2

Something like this (depending on your exact table structure) should work:

UPDATE item SET rating = 
   (SELECT count(*) FROM rates WHERE type 'positive') - 
   (SELECT count(*) FROM rates WHERE type 'negative');

For more information have a look at the MySQL docs .