Too heavy query execution - php

Question

I have a Database with 187840 lines .
When i execute this query i have this message Query execution was interrupted
TOO HEAVY QUERY
SELECT days.day,count(U.sig_name) as number
FROM days
LEFT JOIN linked U ON
days.day = date(timestamp)
AND
U.sig_name REGEXP "^Tester"
GROUP BY days.day;
What is th solution ?

Answer 1

This is your query:
select days.day, count(U.sig_name) as number
from days left join
linked U
on days.day = date(timestamp) AND U.sig_name REGEXP "^Tester"
group by days.day;
You have a problem because of the function call around timestamp. You might find this version better:
select days.day,
(select count(*)
from linked u
where u.timestamp >= days.day an du.timestamp < date_add(days.day, interval 1 day) and
u.sig_name not like '%Tester%'
)
from days;
For performance, you want a composite index on linked(timestamp, sig_name). This eliminates the outer aggregation (the aggregation uses the index instead), and allows an index to be used for the matching.

Answer 2

You can handle massive data using LIMIT:
$limit_size = 10000;
$flag_done = false;
for ($i = 1; ! $flag_done; $i++) {
$queryString = "SELECT days.day,count(U.sig_name) as number from days left join linked U on days.day = date(timestamp) AND U.sig_name REGEXP "^Tester" group by days.day LIMIT $index*$limit_size, $limit_size";
if($result = mysql_query($queryString, $db)){
[WHAT YOU WANT TO DO WITH RESULT HERE]
} else $flag_done = true;
}