rendered paste body# here is the test table.create table cdr ( call_id bigint auto_increment primary key, call_cid varchar(32), call_csid varchar(32), call_start timestamp, call_end timestamp, index call_start_i (call_start), index call_end_i (call_end));# Paste this by hand about 80 times to generate sample data.set @ts:=(now() - interval cast(rand()*1000 as SIGNED) second); insert into cdr VALUES (null, concat('360555', lpad((cast(rand()*1000 as SIGNED)),4,'0')), concat('206555', lpad((cast(rand()*1000 as SIGNED)),4,'0')), @ts, (@ts + interval cast(rand()*1000 as SIGNED) second) );# then query it :)select a.call_start, (select count(call_id) from cdr as b where ( b.call_start <= a.call_start and b.call_end >= a.call_start) ) as 'Simultanious' from cdr as a group by call_start order by Simultanious;# my samplemysql> select * from cdr;+---------+------------+------------+---------------------+---------------------+| call_id | call_cid | call_csid | call_start | call_end |+---------+------------+------------+---------------------+---------------------+| 1 | 3605550653 | 2065550072 | 2005-06-19 10:44:59 | 2005-06-19 10:51:42 || 2 | 3605550784 | 2065550524 | 2005-06-19 10:43:59 | 2005-06-19 10:48:28 || 3 | 3605550064 | 2065550999 | 2005-06-19 10:44:24 | 2005-06-19 10:57:47 || 4 | 3605550691 | 2065550395 | 2005-06-19 10:56:58 | 2005-06-19 11:12:01 || 5 | 3605550937 | 2065550700 | 2005-06-19 10:51:50 | 2005-06-19 11:03:18 || 6 | 3605550642 | 2065550185 | 2005-06-19 10:51:38 | 2005-06-19 10:51:41 || 7 | 3605550279 | 2065550024 | 2005-06-19 10:49:42 | 2005-06-19 10:54:26 || 8 | 3605550885 | 2065550384 | 2005-06-19 10:51:32 | 2005-06-19 10:55:58 || 9 | 3605550099 | 2065550957 | 2005-06-19 10:54:20 | 2005-06-19 11:02:29 || 10 | 3605550413 | 2065550336 | 2005-06-19 10:47:44 | 2005-06-19 10:55:04 || 11 | 3605550655 | 2065550691 | 2005-06-19 10:54:05 | 2005-06-19 11:02:15 || 12 | 3605550418 | 2065550956 | 2005-06-19 10:51:15 | 2005-06-19 11:00:03 || 13 | 3605550275 | 2065550062 | 2005-06-19 10:44:40 | 2005-06-19 10:52:46 || 14 | 3605550765 | 2065550094 | 2005-06-19 10:53:27 | 2005-06-19 10:56:19 || 15 | 3605550389 | 2065550203 | 2005-06-19 10:47:51 | 2005-06-19 11:02:00 || 16 | 3605550640 | 2065550289 | 2005-06-19 10:46:54 | 2005-06-19 10:55:38 || 17 | 3605550193 | 2065550709 | 2005-06-19 10:45:00 | 2005-06-19 11:01:04 || 18 | 3605550582 | 2065550824 | 2005-06-19 10:45:58 | 2005-06-19 10:52:16 || 19 | 3605550946 | 2065550485 | 2005-06-19 10:50:37 | 2005-06-19 11:00:23 || 20 | 3605550631 | 2065550720 | 2005-06-19 10:49:35 | 2005-06-19 11:01:22 || 21 | 3605550762 | 2065550680 | 2005-06-19 10:51:17 | 2005-06-19 10:53:13 || 22 | 3605550352 | 2065550139 | 2005-06-19 10:48:33 | 2005-06-19 10:59:15 || 23 | 3605550030 | 2065550778 | 2005-06-19 10:44:23 | 2005-06-19 10:57:46 || 24 | 3605550982 | 2065550878 | 2005-06-19 10:46:16 | 2005-06-19 10:53:42 || 25 | 3605550630 | 2065550371 | 2005-06-19 10:47:41 | 2005-06-19 11:03:45 || 26 | 3605550643 | 2065550095 | 2005-06-19 10:45:47 | 2005-06-19 10:54:55 || 27 | 3605550621 | 2065550750 | 2005-06-19 10:50:01 | 2005-06-19 11:04:45 || 28 | 3605550208 | 2065550523 | 2005-06-19 10:54:42 | 2005-06-19 11:11:14 || 29 | 3605550984 | 2065550743 | 2005-06-19 10:51:03 | 2005-06-19 11:03:49 || 30 | 3605550699 | 2065550698 | 2005-06-19 10:47:36 | 2005-06-19 10:54:09 || 31 | 3605550176 | 2065550268 | 2005-06-19 10:43:04 | 2005-06-19 10:56:36 || 32 | 3605550845 | 2065550457 | 2005-06-19 10:53:19 | 2005-06-19 11:05:50 || 33 | 3605550678 | 2065550233 | 2005-06-19 10:51:09 | 2005-06-19 10:53:20 || 34 | 3605550388 | 2065550072 | 2005-06-19 10:41:39 | 2005-06-19 10:44:56 || 35 | 3605550254 | 2065550962 | 2005-06-19 10:44:46 | 2005-06-19 10:45:35 || 36 | 3605550661 | 2065550222 | 2005-06-19 10:51:34 | 2005-06-19 10:53:39 || 37 | 3605550423 | 2065550237 | 2005-06-19 10:41:37 | 2005-06-19 10:56:56 || 38 | 3605550650 | 2065550609 | 2005-06-19 10:42:55 | 2005-06-19 10:44:30 || 39 | 3605550965 | 2065550874 | 2005-06-19 10:46:46 | 2005-06-19 10:54:43 || 40 | 3605550387 | 2065550644 | 2005-06-19 10:44:52 | 2005-06-19 10:45:52 || 41 | 3605550657 | 2065550185 | 2005-06-19 10:51:29 | 2005-06-19 11:07:23 || 42 | 3605550218 | 2065550443 | 2005-06-19 10:54:01 | 2005-06-19 11:03:22 || 43 | 3605550705 | 2065550095 | 2005-06-19 10:49:39 | 2005-06-19 10:55:36 || 44 | 3605550445 | 2065550716 | 2005-06-19 10:49:14 | 2005-06-19 10:53:20 || 45 | 3605550679 | 2065550146 | 2005-06-19 10:56:13 | 2005-06-19 11:07:45 || 46 | 3605550046 | 2065550155 | 2005-06-19 10:57:13 | 2005-06-19 11:07:52 || 47 | 3605550728 | 2065550455 | 2005-06-19 10:45:28 | 2005-06-19 10:46:59 || 48 | 3605550178 | 2065550621 | 2005-06-19 10:56:08 | 2005-06-19 11:05:40 || 49 | 3605550276 | 2065550383 | 2005-06-19 10:41:00 | 2005-06-19 10:42:29 || 50 | 3605550223 | 2065550221 | 2005-06-19 10:52:40 | 2005-06-19 10:59:55 || 51 | 3605550262 | 2065550773 | 2005-06-19 10:49:05 | 2005-06-19 10:50:22 || 52 | 3605550110 | 2065550347 | 2005-06-19 10:56:30 | 2005-06-19 11:03:15 || 53 | 3605550710 | 2065550594 | 2005-06-19 10:41:13 | 2005-06-19 10:55:15 || 54 | 3605550614 | 2065550789 | 2005-06-19 10:50:31 | 2005-06-19 10:52:11 |+---------+------------+------------+---------------------+---------------------+54 rows in set (0.00 sec)# output+---------------------+--------------+| call_start | Simultanious |+---------------------+--------------+| 2005-06-19 10:41:00 | 1 || 2005-06-19 10:41:13 | 2 || 2005-06-19 10:41:37 | 3 || 2005-06-19 10:41:39 | 4 || 2005-06-19 10:42:55 | 4 || 2005-06-19 10:43:04 | 5 || 2005-06-19 10:43:59 | 6 || 2005-06-19 10:44:23 | 7 || 2005-06-19 10:44:24 | 8 || 2005-06-19 10:44:40 | 8 || 2005-06-19 10:44:46 | 9 || 2005-06-19 10:44:52 | 10 || 2005-06-19 10:44:59 | 10 || 2005-06-19 10:45:00 | 11 || 2005-06-19 10:45:58 | 12 || 2005-06-19 10:45:28 | 12 || 2005-06-19 10:45:47 | 12 || 2005-06-19 10:46:16 | 13 || 2005-06-19 10:46:46 | 14 || 2005-06-19 10:46:54 | 15 || 2005-06-19 10:47:36 | 15 || 2005-06-19 10:47:41 | 16 || 2005-06-19 10:47:44 | 17 || 2005-06-19 10:47:51 | 18 || 2005-06-19 10:48:33 | 18 || 2005-06-19 10:49:05 | 19 || 2005-06-19 10:49:14 | 20 || 2005-06-19 10:49:35 | 21 || 2005-06-19 10:49:39 | 22 || 2005-06-19 10:56:08 | 23 || 2005-06-19 10:56:58 | 23 || 2005-06-19 10:49:42 | 23 || 2005-06-19 10:56:13 | 24 || 2005-06-19 10:56:30 | 24 || 2005-06-19 10:57:13 | 24 || 2005-06-19 10:50:01 | 24 || 2005-06-19 10:50:31 | 24 || 2005-06-19 10:50:37 | 25 || 2005-06-19 10:51:03 | 26 || 2005-06-19 10:51:09 | 27 || 2005-06-19 10:51:15 | 28 || 2005-06-19 10:54:01 | 28 || 2005-06-19 10:54:42 | 29 || 2005-06-19 10:51:17 | 29 || 2005-06-19 10:53:27 | 29 || 2005-06-19 10:54:05 | 29 || 2005-06-19 10:54:20 | 29 || 2005-06-19 10:51:29 | 30 || 2005-06-19 10:53:19 | 30 || 2005-06-19 10:51:32 | 31 || 2005-06-19 10:52:40 | 31 || 2005-06-19 10:51:34 | 32 || 2005-06-19 10:51:50 | 32 || 2005-06-19 10:51:38 | 33 |+---------------------+--------------+54 rows in set (0.00 sec)