查询执行太重

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 ?

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.

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;
        }