存在查询需要很长时间

Question

From my debian terminal I try to execute in mysql client a query like:

SELECT * 
FROM stop_times_lazio_set2_withtime2 AS B  
WHERE EXISTS 
(SELECT * 
FROM stop_times_lazio_set2_emptytime2 AS A 
WHERE B.trip_id=A.trip_id);

table A contains around 3 million records. table B is a sub set of A of around 400000 records.

I'd like to select every records of A thats have a row "parent" with the same id (yes its not an unique/primary id)

Now it takes more than hours...now I'm around 2h and i still seen just a blinking pointer... is it the query correct? Even I can't access to others mysql client like phpmyadmin. There is any way to speed up the process? There is a way to check how many records are processed at running times?

Answer 1

I guess you have already indexed trip_id ? There is another way writing the query, maybe it helps:

SELECT *
FROM stop_times_lazio_set2_withtime
WHERE trip_id IN (SELECT trip_id FROM stop_times_lazio_set2_emptytime2)

Answer 2

I would expect a straight JOIN to be much much faster...

SELECT B.* 
FROM stop_times_lazio_set2_withtime2 AS B
JOIN stop_times_lazio_set2_emptytime2 AS A ON B.trip_id=A.trip_id

Answer 3

Why not using a simpler request ?

SELECT A.* 
FROM stop_times_lazio_set2_emptytime2 AS A, stop_times_lazio_set_withtime2 AS B
WHERE B.trip_id=A.trip_id;

With that many records, it will obviously take time.

You can actually prevent it by processing only a few at a time by adding this at the end of the request

LIMIT <beginning>, <number of records>

Answer 4

Did you tried "left join"??

sample:

select columns from withtime 
  left join emptytime on withtime.tripid=emptytime.tripid;