I think what you're trying to accomplish is well-documented here, as a special case of the outerjoin function.
For example, consider your table A
A = table({'a' 'b' 'c' 'e' 'h'}',[1 2 3 11 17]',...
'VariableNames',{'Key1' 'Var1'})
Key1 Var1
____ ____
'a' 1
'b' 2
'c' 3
'e' 11
'h' 17
And now consider another table B
B = table({'a','b','d','e'}',[4;5;6;7],...
'VariableNames',{'Key1' 'Var2'})
Key1 Var2
____ ____
'a' 4
'b' 5
'd' 6
'e' 7
Notice that the first column in both tables has some entries in common with the other and some not. This is a direct analogy to your weekday and all days example.
C = outerjoin(A,B,'MergeKeys',true)
After this, your table C will have the merged dataset/table.
Key1 Var1 Var2
____ ____ ____
'a' 1 4
'b' 2 5
'c' 3 NaN
'd' NaN 6
'e' 11 7
'h' 17 NaN
Here you can explore more options in the outerjoin documentation to filter your data into exactly one column if needed.
