MySQL Query Optimization – Is There a Soft ORDER BY / GROUP BY?

MySQLmysql-5.1order-byquery

SQL-Fiddle

http://sqlfiddle.com/#!9/c82c87b/1

Table Definition

First of all, this is my table:

 CREATE TABLE `stackoverflow` (
`id` VARBINARY( 36 ) NOT NULL COMMENT 'GUID generated by PHP',
`time` TIME NOT NULL COMMENT 'Current time(stamp)',
`type` VARCHAR( 10 ) NOT NULL COMMENT 'start/stop',
`reference` VARBINARY( 36 ) NOT NULL COMMENT 'multiple starts/stops to one reference',
PRIMARY KEY ( `id` )
) ENGINE = MYISAM

Data

This is some example-data:

INSERT INTO `stackoverflow` (
`id` ,
`time` ,
`type` ,
`reference`
)
VALUES 
('03bd8e91-b9aa-4d18-be47-9e9cce903cfd', '11:00:00', 'start', '76afe924-08aa-431b-904a-66290c50da6a'), 
('ef10860a-7666-4ca0-95b6-79ef2d5b3f75', '11:01:00', 'start', 'fd064ef5-462f-489c-ae14-3cb766eb80c4'), 
('9bc72e24-a0d4-43a3-86ab-973c331e2958', '11:02:00', 'stop', 'fd064ef5-462f-489c-ae14-3cb766eb80c4'), 
('a245cda3-1196-4dba-832e-0474fd0eb0bf', '11:03:00', 'start', '05324e7b-a358-48bb-9779-08cf60038bb8'), 
('488c67e6-c21d-4356-9578-49e857259345', '11:06:00', 'stop', '76afe924-08aa-431b-904a-66290c50da6a'), 
('11c0e4ac-e7e9-418a-841f-650ced3e8343', '11:12:00', 'stop', '05324e7b-a358-48bb-9779-08cf60038bb8');

It is basically about timers – every timer (reference) has multiple starts and stops. Every entry is either a start or a stop.

Querying Data

To display these timers in HTML, I need to order the data like this:

SELECT * FROM stackoverflow ORDER BY reference DESC, time ASC;

The result looks like this:

  ef10860a-7666-4ca0-95b6-79ef2d5b3f75  11:01:00    start   fd064ef5-462f-489c-ae14-3cb766eb80c4
  9bc72e24-a0d4-43a3-86ab-973c331e2958  11:02:00    stop    fd064ef5-462f-489c-ae14-3cb766eb80c4
# 03bd8e91-b9aa-4d18-be47-9e9cce903cfd  11:00:00    start   76afe924-08aa-431b-904a-66290c50da6a
# 488c67e6-c21d-4356-9578-49e857259345  11:06:00    stop    76afe924-08aa-431b-904a-66290c50da6a
  a245cda3-1196-4dba-832e-0474fd0eb0bf  11:03:00    start   05324e7b-a358-48bb-9779-08cf60038bb8
  11c0e4ac-e7e9-418a-841f-650ced3e8343  11:12:00    stop    05324e7b-a358-48bb-9779-08cf60038bb8

Questions

  • How do I get the rows, marked with a # into first position?

  • I think ordering by reference is wrong, but how do I keep them together? Just ordering by time would produce wrong results. It would be great, if these pairs of references could stay together.

  • Do I need a virtual table or a sub-query?

Additional information

Meanwhile I fixed this “‘SQL’ problem” in PHP with multiple separate SQL operations, as detailed below:

  1. get all references

    SELECT DISTINCT reference FROM stackoverflow;

  2. for each reference

    SELECT * FROM stackoverflow WHERE reference = :reference ORDER BY time;

  3. for each row
    -> generate HTML "timer"

    Result:

    # 03bd8e91-b9aa-4d18-be47-9e9cce903cfd  11:00:00    start   76afe924-08aa-431b-904a-66290c50da6a
# 488c67e6-c21d-4356-9578-49e857259345  11:06:00    stop    76afe924-08aa-431b-904a-66290c50da6a
  ef10860a-7666-4ca0-95b6-79ef2d5b3f75  11:01:00    start   fd064ef5-462f-489c-ae14-3cb766eb80c4
  9bc72e24-a0d4-43a3-86ab-973c331e2958  11:02:00    stop    fd064ef5-462f-489c-ae14-3cb766eb80c4
  a245cda3-1196-4dba-832e-0474fd0eb0bf  11:03:00    start   05324e7b-a358-48bb-9779-08cf60038bb8
  11c0e4ac-e7e9-418a-841f-650ced3e8343  11:12:00    stop    05324e7b-a358-48bb-9779-08cf60038bb8

The order is now as expected – it would still be great if there is a MySQL solution for this. 🙂

Note: The exact MySQL version is 5.1.61.

Best Answer

SELECT s.* 
FROM stackoverflow s, ( SELECT reference, MIN(time) time
                        FROM stackoverflow
                        GROUP BY reference
                       ) o
WHERE s.reference = o.reference
ORDER BY o.time ASC, reference DESC, time ASC;

fiddle

Everything is simple. You want to sort groups by the datetime of the most aged record in the group. The subquery obtains this info, and it is used in main query by joining it to each record in a group. For to understand replace s.* with * in output and analyze the result.

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