Hi Betram,
What you are asking for is to combine the results in ITAB1 and LT_TAB. This does not mean joining two table types.
To achieve what you are looking for, you will need to declare one more Table Type and a corresponding internal table, say LT_JOIN, which contains all the UNIQUE columns from ITAB1 and LT_TAB.
Also, to be noted is that you would need a common key connecting both ITAB1 and LT_TAB, as in a common column, based on which you can join them.
Once the pre-requisites are set, you need to loop at the parent table and read the second table with the common key, then populate the new table.
e.g.: Assuming ITAB1 is the parent.
LOOP AT itab1 INTO wa_itab1.
READ TABLE lt_tab INTO ls_tab WITH KEY column = wa_itab1-column.
IF sy-subrc EQ 0.
ls_join-column1 = wa_itab1-column1.
ls_join-column2 = wa_itab1-column2.
ls_join-column3 = wa_itab1-column2.
ls_join-column4 = wa_itab1-column3.
ls_join-column5 = ls_tab-column1.
ls_join-column6 = ls_tab-column2.
ls_join-column7 = ls_tab-column3.
ls_join-column8 = ls_tab-column4.
APPEND ls_join INTO lt_join.
ENDIF.
CLEAR: ls_join,
wa_itab1,
ls_tab.
ENDLOOP.
Hope this helps.