PostgreSQL: insert from another table

Question

I\'m trying to insert data to a table from another table and the tables have only one column in common. The problem is, that the TABLE1 has columns that won\'t accept null value

Answer 1

For referential integtity :

insert into  main_tbl (col1, ref1, ref2, createdby)
values ('col1_val',
        (select ref1 from ref1_tbl where lookup_val = 'lookup1'),
        (select ref2 from ref2_tbl where lookup_val = 'lookup2'),
        'init-load'
       );