itab is not initial

1)

what this mean itab is not initial

if itab1[] is not initial

itab2 = itab1

is that mean itab1 has no record enter into loop ?

2)

im having two itabs: itab1 and  itab2 and itab3 with different struct i.e having two itabs field

select query fetching records into itab1 with werks (mandt) as input field

itab1 having vbeln werks matnr netwr from vbap

select query fetching records into itab2 with kunnr as input field

itab2 having vbeln aurt from vbak

i dont want to use inner join

i want to to put my itab1 and itab 2 record into itab 3 (itab3 having combine structure of all two itabs field)

itab3 im assign to alv