Add Time Together From Previous Row in Microsoft Access - sql

Question

I am using Microsoft Access 2016 and I have a table where the goal is using the provided start time for each date, add the given Slot to the Start to calculate the End time. Where I am having difficulties is where Start is null, it is to pull the previous records' End time as its Start time and repeat the process.
Below is a sample table of data:
Day
PrimaryKey
AbovePrimaryKey
Start
Slot
End
9/19/2022
171
4:00:00 PM
2:30
9/19/2022
172
171
2:30
9/19/2022
173
172
1:30
9/20/2022
174
173
11:00:00 AM
1:30
9/20/2022
175
174
1:30
9/20/2022
176
175
2:30
9/20/2022
177
176
2:30
9/20/2022
178
177
1:00
9/20/2022
179
178
1:00
Below is what I am wanting as the result:
Day
PrimaryKey
Start
Slot
End
9/19/2022
171
4:00:00 PM
2:30
6:30:00 PM
9/19/2022
172
6:30:00 PM
2:30
8:30:00 PM
9/19/2022
173
8:30:00 PM
1:30
10:00:00 PM
9/20/2022
174
11:00:00 AM
1:30
12:30:00 PM
9/20/2022
175
12:30:00 PM
1:30
2:00:00 PM
9/20/2022
176
2:00:00 PM
2:30
4:30:00 PM
9/20/2022
177
4:30:00 PM
2:30
7:00:00 PM
9/20/2022
178
7:00:00 PM
1:00
8:00:00 PM
9/20/2022
179
8:00:00 PM
1:00
9:00:00 PM
I was able to get the previous row's primary key to use in reference in some subquery to pull the previous row's End, but am unable to determine how to do so, especially since I have also have to calculate Start and End.
Any help would be greatly appreciated. Thank you.

Answer 1

You can do this with four sets of subqueries:
SELECT
SampleData.Day,
SampleData.PrimaryKey,
(Select S2.Start
From SampleData As S2
Where S2.PrimaryKey =
(Select Max(S.PrimaryKey)
From SampleData As S
Where S.Start Is Not Null And S.PrimaryKey <= SampleData.PrimaryKey)) +
(Select CDate(IIf(Sum(S3.Slot) Is Null, #00:00#, Sum(S3.Slot)))
From SampleData As S3
Where S3.PrimaryKey < SampleData.PrimaryKey And S3.PrimaryKey >=
(Select Max(S.PrimaryKey)
From SampleData As S
Where S.Start Is Not Null and S.PrimaryKey <= SampleData.PrimaryKey)) As [Start],
SampleData.Slot,
(Select S2.Start
From SampleData As S2
Where S2.PrimaryKey =
(Select Max(S.PrimaryKey)
From SampleData As S
Where S.Start Is Not Null And S.PrimaryKey <= SampleData.PrimaryKey)) +
(Select CDate(Sum(S3.Slot))
From SampleData As S3
Where S3.PrimaryKey <= SampleData.PrimaryKey And S3.PrimaryKey >=
(Select Max(S.PrimaryKey)
From SampleData As S
Where S.Start Is Not Null And S.PrimaryKey <= SampleData.PrimaryKey)) As [End]
FROM
SampleData;
Output: