Problem description & analysis:

Here is a categorized detail table:

We need to group the table and concatenate the detail data using the semicolon.

Solution:

Use SPL XLL to do this:

=spl("=E@b(?.groups(~1;concat(~2;$[;])))",A2:B9)

As shown in the picture below:

Explanation:

E@b function converts the two-dimensional table to a sequence. ~1 represents the first sub-member of the current member; and $[] represents a string.