MySql查询的执行永远需要PHP来完成，但是从phpMyAdmin运行时很快就会完成

Question

I have a sql querying a MySql table having millions of records. This gets executed in phpMyAdmin in around 2 secs but when run from PHP script, it doesn't complete executing.

select 
  concat(p1.`Date`," ",p1.`Time`) as har_date_from,
  concat(p2.`Date`," ",p2.`Time`) as har_date_to,
 (select concat(p3.`Date`," ",p3.`Time`) from 
   power_logger p3 
   where p3.slno between 1851219 and 2042099
   and p3.meter_id="logger1"
   and str_to_date(concat(p3.`Date`," ",p3.`Time`),"%d/%m/%Y %H:%i:%s") >=
       str_to_date(concat(p1.`Date`," ",p1.`Time`),"%d/%m/%Y %H:%i:%s")

   order by p3.slno limit 1) as cur_date_from,
     (select concat(p4.`Date`," ",p4.`Time`) from
        power_logger p4 
        where p4.slno between 1851219 
        and 2042099
        and p4.meter_id="logger1" 
        and str_to_date(concat(p4.`Date`," ",p4.`Time`),"%d/%m/%Y %H:%i:%s") >=
            str_to_date(concat(p2.`Date`," ",p2.`Time`),"%d/%m/%Y %H:%i:%s")
        order by p4.slno 
        limit 1
      )
      as cur_date_to, 
      p1.THD_A_N_Avg-p2.THD_A_N_Avg as thd_diff
      from power_logger p1
    join 
      power_logger p2 
        on p2.slno=p1.slno+1 
        and p1.meter_id="fluke1" 
        and p2.meter_id=p1.meter_id
        and p1.slno between 2058609 and 2062310 
        and p1.THD_A_N_Avg-p2.THD_A_N_Avg>=2.0000

php script: $query=/*The query above passed as string*/ $mysql=mysql_connect('localhost','username','pwd') or die(mysql_error()); mysql_select_db('dbname',$mysql); $rows=mysql_query($query,$mysql) or die(mysql_error()); $query=/*The query above passed as string*/ $mysql=mysql_connect('localhost','username','pwd') or die(mysql_error()); mysql_select_db('dbname',$mysql); $rows=mysql_query($query,$mysql) or die(mysql_error());

There are no issues in mysql connectivity and related stuffs, as I run a lot of other queries successfully. I have set indexes on meter_id and Date,Time together. slno is the auto increment value. I know there are similar questions asked as I found a lot from my research but none of them really helped me. Thanks in advance if anybody could help me out to find a solution.

Query Description:This queries the power_logger table containing millions of records and THD_A_N_AVG, meter_id,slno,Date and Time are among the columns of the table. This selects The date and time from two consecutive rows with in a range of slnos where difference between THD_A_N_AVG is greater than or equal to 2. When those dates are fetched, it even has to fetch the date and time with in a different range of slnos where the date and time are the closest to the once fetched earlier thus forming har_date_from,har_date_to, cur_date_from,cur_date_to. What messes up here is the nested select.

Answer 1

Usually PHPMyAdmin automatically adds "LIMIT 0, 30" at the end of the query, so you only load 30 rows at once. In your code you are trying to load everything at once, that's why it's taking so long.