MYSQL - 用下一个日期更新临时表

Question

I have a table with columns EquipmentNo (VARCHAR), ActionType (VARCHAR) and ActionDate (DateTime)

When a user checks out some equipment a row would be added like this:

EquipmentNo: 123
ActionType: 'checkout'
ActionDate: '2017-02-03 09:05:27'

And when they check that equipment back in:

EquipmentNo: 123
ActionType: 'checkin'
ActionDate: '2017-02-03 10:32:46'

A single piece of equipment can be checked out/checked in multiple times a day, so lets say EquipmentNo 123 had another checkout/check in later on the same day.

EquipmentNo: 123
ActionType: 'checkout'
ActionDate: '2017-02-03 11:15:27'

EquipmentNo: 123
ActionType: 'checkout'
ActionDate: '2017-02-03 11:30:55'

I need to write a query which calculates the duration of all sessions (difference between checkout and corresponding check in time). the query needs to also sum up how many sessions that equipment has had, in our case it had 2 sessions with a duration of 102 minutes.

Here is what I have so far

CREATE TEMPORARY TABLE IF NOT EXISTS tmp1 AS (
SELECT EquipmentNo, MIN( ActionDate ) AS CheckOutDate, 
NULL AS CheckInDate, COUNT( * ) AS Sessions
FROM EquipmentSessions WHERE ActionType =  'checkout' GROUP BY EquipmentNo, ActionDate);

This yields something like

123 | 2017-02-03 09:05:27 | NULL | 1
123 | 2017-02-03 11:15:27 } NULL | 1

What I cannot seem to do is workout how to structure my update statement to use this table as the source and basically say "get the next check in date after sourceTable.CheckOutDate for each EquipmentNo".

Answer 1

Let's say the table contents look like follows:

CREATE TABLE eqp (eno int, action_type varchar(20), action_date timestamp);

INSERT INTO eqp VALUES(124, 'checkout', '2017-02-03 09:00:00');
INSERT INTO eqp VALUES(123, 'checkout', '2017-02-03 09:05:27');
INSERT INTO eqp VALUES(124, 'checkin',  '2017-02-03 10:00:00');
INSERT INTO eqp VALUES(123, 'checkin',  '2017-02-03 10:32:46');
INSERT INTO eqp VALUES(123, 'checkout', '2017-02-03 11:15:27');
INSERT INTO eqp VALUES(123, 'checkin',  '2017-02-03 11:30:55');

INSERT INTO eqp VALUES(123, 'checkout', '2017-02-04 09:00:00');
INSERT INTO eqp VALUES(123, 'checkin',  '2017-02-04 10:00:00');
INSERT INTO eqp VALUES(123, 'checkout', '2017-02-04 15:00:00');
INSERT INTO eqp VALUES(123, 'checkin',  '2017-02-04 17:00:00');
INSERT INTO eqp VALUES(123, 'checkout', '2017-02-04 18:30:00');
INSERT INTO eqp VALUES(123, 'checkin',  '2017-02-04 19:00:00');

So, assuming the following:

• checkout will always precede checkin for an equipment
• Both the actions will be completed within the same day, AND
• (An implied assumption) Every equipment that is checked out will have a check in record in the table (before this desired operation is performed)

We can write a single query to fetch all checkout events sorted first by equipment and then by time, in the order that they occurred, and assign a rank to every record fetched:

SELECT @checkoutrank := @checkoutrank + 1 AS rank, eno, action_type, action_date
    FROM eqp, (SELECT @checkoutrank := 0) r
WHERE action_type='checkout'
ORDER BY eno ASC, action_date ASC

This gives:

 rank   |   eno     | action_type   |   action_date
----------------------------------------------------------
1       |   123     |  checkout     | 2017-02-03 09:05:27
2       |   123     |  checkout     | 2017-02-03 11:15:27   
3       |   123     |  checkout     | 2017-02-04 09:00:00
4       |   123     |  checkout     | 2017-02-04 15:00:00   
5       |   123     |  checkout     | 2017-02-04 18:30:00
6       |   124     |  checkout     | 2017-02-03 09:00:00

A similar query can then be written for checkin too.

We shall then have two tables — with corresponding checkout and checkin in the comparable order — and in the sequence that they occurred, thereby giving us start and end time for each individual session for the equipments. These two corresponding tables could now simply be joined over rank and eno (equipment number) where we can compute the count of sessions as well as SUM up the time difference between each checkout and checkin :

SELECT checkin.eno, DATE(checkin.action_date) AS session_date, 
    COUNT(*) AS sessions, 
    SUM(TIMESTAMPDIFF(SECOND, checkout.action_date, checkin.action_date)) 
             AS sesssion_duration
FROM
    (
        SELECT @checkoutrank := @checkoutrank + 1 AS rank, eno, action_type, action_date
            FROM eqp, (SELECT @checkoutrank := 0) r
        WHERE action_type='checkout'
        ORDER BY eno ASC, action_date ASC
    ) checkout

INNER JOIN
    (
        SELECT @checkinrank := @checkinrank + 1 AS rank, eno, action_type, action_date
            FROM eqp, (SELECT @checkinrank := 0) r
        WHERE action_type='checkin'
        ORDER BY eno ASC, action_date ASC
    ) checkin

    ON checkout.rank = checkin.rank
    AND checkout.eno = checkin.eno

GROUP BY checkin.eno, DATE(checkin.action_date)

Giving us the output as:

eno     | session_date  |   sessions    |   session_duration
--------------------------------------------------------------
123     |   2017-02-03  |       2       |   6167
123     |   2017-02-04  |       3       |   12600
124     |   2017-02-03  |       1       |   3600

The session_duration above is computed in SECOND s for the sake of simplicity as well as accuracy.

Demo link .