MySQL – Extract All Links Table

That's because you're using a CHAR column type; this is a fixed-width column; regardless of how much data you put in there, it'll always take up exactly that number of characters in the data store. It is designed for columns where you'll always have exactly that number of characters, because it's more efficient in that specific case.

What you want in your case is VARCHAR; it'll make a note in the column data of how many characters you're storing, and only take up that amount of space in the data store.

Supposing id is primary_key and auto increment column for both t1 and t2, I think this is what you need:

CREATE TRIGGER trig1
AFTER INSERT ON t1
FOR EACH ROW 
BEGIN
  IF @latitude = NEW.latitude AND @longitude = NEW.longitude THEN
     SET @end_time = NEW.received_time;
     SET @iddle_time = TIMEDIFF(NEW.received_time, @start_time);
     UPDATE t2 SET iddle_time = @iddle_time, end_time = @end_time
               WHERE id = @last_id_t2;
  ELSE

     INSERT INTO t2 VALUES (NULL, NEW.uid, NEW.latitude, NEW.longitude, 
                            NULL, NEW.imno, NEW.received_time, NEW.received_time);       
     SET @last_id_t2 = LAST_INSERT_ID();
     SET @latitude = NEW.latitude; SET @longitude = NEW.longitude;
     SET @iddle_time = NULL;
     SET @start_time = NEW.received_time; SET @end_time = NEW.received_time;
  END IF;
END;

You can see the whole scheme here : http://sqlfiddle.com/#!2/a70ac/1