can i insert row on database table without define Primary key

hello abap-ers ,

i create a screen (module-pool) with Push-button that code is insert in database table as shown

primary key id ( that's my question)

time is default with sy-uzeit ( give me the current time in server )

tables : zdb.

data wa type zdb.

wa-time = sy-uzeit .

insert zdb from wa.

if sy-subrc = 0.

message wa-id type 'I' .

else.

message 'ERROR' type 'I'.

this code is working only one time at first .

the Ques is :

can i insert the time field without primary key (ID) <ID can increment automatically> ???