如何在mysql中使用SUM和GROUP BY更新包含在另一个查询中的记录

Question

I am having a mysql table

content_votes_tmp

+------------+------------------+------+-----+---------+----------------+
| Field      | Type             | Null | Key | Default | Extra          |
+------------+------------------+------+-----+---------+----------------+
| up         | int(11)          | NO   | MUL | 0       |                |
| down       | int(11)          | NO   |     | 0       |                |
| ip         | int(10) unsigned | NO   |     | NULL    |                |
| content    | int(11)          | NO   |     | NULL    |                |
| datetime   | datetime         | NO   |     | NULL    |                |
| is_updated | tinyint(2)       | NO   |     | 0       |                |
| record_num | int(11)          | NO   | PRI | NULL    | auto_increment |
+------------+------------------+------+-----+---------+----------------+

surfers can vote up or vote down on posts ie content, a record gets inserted everytime a vote is given same as rating , in the table along with other data like ip , content id

Now i am trying to create cronjob script in php which will SUM(up) and SUM(down) of votes

like this,

mysqli_query($con, "SELECT  SUM(up) as up_count,  SUM(down) as down_count, content FROM `content_votes_tmp` WHERE is_updated = 0 GROUP by content")

and then by using while loop in php i can update the main table for the specific content id,

but i would like to set the records which are part of SUM to be marked as updated ie SET is_updated = 1 , so the same values wont get summed again and again.

How can i achieve this ? using mysql query ? and work on same data set as , every second/milisecond the records are getting inserted in the table ,.

---

i can think of another way of achieving this is by getting all the non-updated records and doing sum in the php and then updating every record.

Answer 1

The simplest way would probably be a temporary table. Create one with the record_num values you want to select from;

CREATE TEMPORARY TABLE temp_table AS
  SELECT record_num FROM `content_votes_tmp` WHERE is_updated = 0;

Then do your calculation using the temp table;

SELECT  SUM(up) as up_count,  SUM(down) as down_count, content 
FROM `content_votes_tmp` 
WHERE record_num IN (SELECT record_num FROM temp_table) 
GROUP by content

Once you've received your result, you can set is_updated on the values you just calculated over;

UPDATE `content_votes_tmp`
SET is_updated = 1
WHERE record_num IN (SELECT record_num FROM temp_table)

If you want to reuse the connection to do the same thing again, you'll need to drop the temporary table before creating it again, but if you just want to do it a single time in a page, it will disappear automatically when the database is disconnected at the end of the page.