MySQL 5.7

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create table patient (dateOfCheckup date, duration varchar(20))
insert into patient values('2020-05-28', '30 min');
insert into patient values('2020-05-29', '30 min');
insert into patient values('2020-05-30', '1 hour');
insert into patient values('2020-06-03', '1 hour 30 min');
insert into patient values('2020-06-05', '30 min');
insert into patient values('2020-07-21', '1 hour 30 min');
insert into patient values('2020-07-22', '30 min');
insert into patient values('2020-07-28', '1 hour 30 min');
select
dateOfCheckup,
duration,
@cur_dur := ((case when duration like '% hour%' then substring_index(duration, ' hour', 1) * 60 else 0 end) +
(case when duration like '%min%' then substring_index(substring_index(duration, ' min', 1), ' ', -1) + 0 else 0 end)) as minutes,

CASE WHEN @year_month = date_format(dateOfCheckup, '%Y-%m')
     THEN @cum_sum := @cum_sum + @cur_dur
     ELSE @cum_sum := @cur_dur
     END total,
@year_month := date_format(dateOfCheckup, '%Y-%m') monthOfCheckup

from patient, (SELECT @year_month:='', @cum_sum:=0, @cur_dur:=0) variables
ORDER BY dateOfCheckup


dateOfCheckup
duration
minutes
total
monthOfCheckup


2020-05-28
30 min
30
30
2020-05

2020-05-29
30 min
30
60
2020-05

2020-05-30
1 hour
60
120
2020-05

2020-06-03
1 hour 30 min
90
90
2020-06

2020-06-05
30 min
30
120
2020-06

2020-07-21
1 hour 30 min
90
90
2020-07

2020-07-22
30 min
30
120
2020-07

2020-07-28
1 hour 30 min
90
210
2020-07

dateOfCheckup	duration	minutes	total	monthOfCheckup
2020-05-28	30 min	30	30	2020-05
2020-05-29	30 min	30	60	2020-05
2020-05-30	1 hour	60	120	2020-05
2020-06-03	1 hour 30 min	90	90	2020-06
2020-06-05	30 min	30	120	2020-06
2020-07-21	1 hour 30 min	90	90	2020-07
2020-07-22	30 min	30	120	2020-07
2020-07-28	1 hour 30 min	90	210	2020-07