Use value if entry is missing compared to another table

Hi all,

I have a table with SLA information. This table, however, only contains objects with violations per every hour, not those without. The table basically looks like that:

StateChanges:

ServerName;DateTime;HealthyPercent;CriticalPercent

serverA;2018-02-18 0:00;95;5

serverB;2018-02-18 0:00;90;10

serverC;2018-02-18 0:00;0;100

serverA;2018-02-18 1:00;90;10

serverC;2018-02-18 1:00;0;100

...

As you see, serverB had a violation at 0:00 but is missing at 1:00 because it was available at 100%. serverD is missing at all.

Further, I have another table where all servers are listed:

GroupTable:

ServerName;

serverA;

serverB;

serverC;

serverD;

...

What I am searching for is a way to show serverB with 100% healthy at every time where there was no validation. Since the time is a sliding window (last 3 months) it cannot be a fixed table and needs to be something calculated "on the fly".

Those computers without any entry in the first table should show 100% healthy.

At the end I am expecting data like (with the bold ones calculated):

ServerName;DateTime;HealthyPercent;CriticalPercent

serverA;2018-02-18 0:00;95;5

serverB;2018-02-18 0:00;90;10

serverC;2018-02-18 0:00;0;100

serverD;2018-02-18 0:00;100;0

serverA;2018-02-18 1:00;90;10

serverB;2018-02-18 1:00;100;0

serverC;2018-02-18 1:00;0;100

serverD;2018-02-18 1:00;100;0

...