select rows where timestamp is a multiple of n seconds

Question

I am logging live data to a database where it is then selected by a php script and posted to a graph on a webpage.

A new datapoint is added every second and I have been graphing the most recent 300 points for a 5 minute history on the graph using the following:

SELECT * FROM table_name ORDER BY timestamp DESC LIMIT 300;

What I would like to do is add functionality to zoom out the data, losing resolution but showing a longer history but selecting every 5th row for example. However if I just select the most recent 300 5th entries the graph 'snakes' across the page as the values I am asking for are different each time as shown:

query 1 entries: [8:00] [7:55] [7:50] [7:45] [7:40] ...
query 2 entries: [8:01] [7:56] [7:51] [7:46] [7:41] ...

where what I want to do is

query 1 entries: [8:00] [7:55] [7:50] [7:45] [7:40] ...
query 1 entries: [8:05] [8:00] [7:55] [7:50] [7:45] ...

I have been looking for a way to do something like

SELECT * FROM table_name WHERE timestamp IS MULTIPLE OF 5 SECONDS

but have had no luck so here I am.

Answer 1

something like

select * from table where MOD(UNIX_TIMESTAMP(timestamp),300)) = 0;

should do the job. But I am not sure if this is correct. The idea is to try to modulo divide the minute part evenly. Be aware, that this may cause in a full table scan

Answer 2

is your query1 and query2 are query from 1 table only? try to use this if you want to get query2 = query1 value + 5mins

SELECT * FROM table_name where timestamp = query1 + INTERVAL 5 MINUTE;