Creating an aggregate function filtered by entry value

Question

Can anyone help me parse an aggregate function for Qgis 2.18 which sums the values of one field, for all entries which match a value of the entry in question.

So, for example if I have a simple layer with field "group", and "value", and entries are;

Group,Value
1,3
1,4
1,5
2,3
2,5
2,6

I want an expression which will yield "Group Total" such that,

Group,Value,Group Total
1,3,12
1,4,12
1,5,12
2,3,14
2,5,14
2,6,14

Next to all the entries in group 1 is the sum of all group 1, next to all the entries in group 2 is the sum of group 2

EDIT - I should add I've tried the most obvious sum("Value", "Group"), the predicted output in the expression calculator shows correct, but in the table the values are all just NULL, so I presume I'm doing something wrong.

EDIT2 - I should also have added that I'm looking for this function to automatically update somehow, in a virtual field, otherwise every time some value changes in my layer (and things do change!) all the totals will be wrong.

• Joseph: This issue has been reported but still seems to be a problem with some QGIS 2.18 versions. It works with QGIS 3.x however.

Answer 1

1. Processing " Statistic by category" enter image description here

2. Join by attibute enter image description here

Result:

enter image description here

• user39790: Thank you for your suggestion, but I'm actually looking for a field which will automatically update, like virtual fields, so I don't think creating a new layer from it will work. I should have been clearer in the question, and have now edited it.