best way to select random row of database of 100k+ in size

[krispykreme]

random selection of one row is what i want right now

 

no filtering needed, but in the future i want to be able to randomly select from a user that has been offline for 24 hours givin a time contraint

 

what would be the best way to do this?  ive never done a random selection in a query so i want to be guided to the best way from the start

[pocobueno1388]

Here is an example of selecting one random row

 

SELECT * FROM table ORDER BY RAND() LIMIT 1

[krispykreme]

this method seems to look at all of the rows?

 

id  select_type  table  type  possible_keys  key  key_len  ref  rows  Extra 

1 SIMPLE users ALL NULL NULL NULL NULL 70064 Using temporary; Using filesort

 

[pocobueno1388]

It only returns one row, correct? You can replace the '*' with whatever columns you need. I'm not sure if thats what you were talking about though.

[krispykreme]

na i mean it goes through 70,000 rows just to get that one row

 

it isnt a huge issue, but if somehow this became 7,000,000 rows it would possibly be and i didnt know if there was a more optimized way = /

[powerspike]

a hackisk way to get it done, would be to get the amount rows in the table, like "select row_id from table where order by row_id DESC limit 0,1";

 

then do a "select * from table where row_id = " . rand(0,$row_id) . "' limit 0,1";

($row_id would be the row_id from the first query).

 

As i said, it's a hackish way, i'm quite sure there is a better way to do it thou.

 

PS, this assumes you have a row_id and it's in some type of order.

 

[AndyB]

read the 'sticky' at the top of this forum!!

 

http://www.phpfreaks.com/forums/index.php/topic,125759.0.html