SQL Server 2014

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CREATE TABLE ticket
(
  ticket_id INTEGER NOT NULL,
  working_time VARCHAR (30) NULL DEFAULT NULL CHECK (working_time != '')
);
INSERT INTO ticket VALUES (18, '20.02.2021,15:00,17:00');
INSERT INTO ticket VALUES (18, '20.02.2021,15:00,17:00');
INSERT INTO ticket VALUES (18, '20.02.2021,15:00,17:00');

INSERT INTO ticket VALUES (20, '20.02.2021,12:00,14:15');
INSERT INTO ticket VALUES (20, '_rubbish__');
INSERT INTO ticket VALUES (20, '20.02.2021,12:00,14:15');
INSERT INTO ticket VALUES (20, NULL);

INSERT INTO ticket VALUES (20, '21.02.2021,12:00,14:15');
INSERT INTO ticket VALUES (20, '_rubbish__');
INSERT INTO ticket VALUES (20, '21.02.2021,12:00,14:15');
INSERT INTO ticket VALUES (20, NULL);
11 rows affected

alter table ticket add WorkingDate as Try_convert(date,Concat(Substring(working_time, 7, 4),SUBSTRING(working_time, 4, 2),SUBSTRING(working_time, 1, 2)),112) persisted;
alter table ticket add WorkingDuration as  DateDiff(minute,Try_convert(time,Substring (working_time, 12, 5),114 ) , Try_convert(time, Substring (working_time, 18, 5),114 )) persisted;
create clustered index Ix_Id_WorkingDuration on ticket(ticket_id,workingdate);
with w as (
	select ticket_Id, workingDate, Sum(workingDuration) d
	from
	ticket
	group by ticket_id, workingDate
)
select ticket_id, workingdate as [The date], FORMAT(d / 60 * 100 + d % 60, '#:0#')
from w
where d>0


ticket_id
The date
(No column name)


18
2021-02-20
6:00

20
2021-02-20
4:30

20
2021-02-21
4:30


Warning: Null value is eliminated by an aggregate or other SET operation.