Assigning grouptext to groupvalue

[#1]

Hello QVer,
I can't find the right searchword which can solve this:
I have TABLE1:
G_FIRST  | G_LAST | G_GROUP  | G_GROUPTEXT  |
A00         | A04        | A00-A04      | A00A04              |
A15         | A18        | A15-A18      | A15A18              |
B20         | B24        | B20-B24      | B20B24              |
B25         | B28        | B25-B28      | B25B28              |          

The other TABLE2 has all dedicated (from first to last) groupvalues in field (F1).
A new field (F_GROUPTEXT) in this TABLE2 should assign G_GROUPTEXT to each value corresponding to a group as defined in TABLE1:

F1   | F_Grouptext |
A00 | A00A05       |
A01 | A00A05       |
A02 | A00A05       |
A03 | A00A05       |
A04 | A00A05       |
A15 | A15A18       |
A16 | A15A18       |
A17 | A15A18       |
A18 | A15A18       |
B20 | B20B24       |
B21 | B20B24       |
B22 | B20B24       |
B23 | B20B24       |
B24 | B20B24       |
and so on.

Can somebody help me to solve this problem without doing it handmade. Thanks.
greetings dj_skbs