Retrieving auto-generated keys for an INSERT statement
There are several ways of doing this in Db2 for LUW.

Firstly, there is a function IDENTITY_VAL_LOCAL() that returns one most recently assigned identity value; it can be used when inserting single records:

insert into parent_tab (some_column) values ('foobar');
insert into child_tab (parent_id, some_other_col) 
  values (identity_val_local(), 42);


assuming parent_tab in the example has an identity column id.

Another option is to use a data change table:

with parent_res (parent_id) as (
  select id from final table (
    insert into parent_tab (some_column) values ('foobar')
  )
)
insert into child_tab (parent_id, some_other_col) 
select parent_id, 42 from parent_res;


The data change table will contain as many rows as are affected by the corresponding DML statement.

In Postgres a similar result can be achieved by using the RETURNING clause of the INSERT statement:

with parent_res (parent_id) as (
  insert into parent_tab (some_col) values ('foo') returning id
)
insert into child_tab (parent_id, some_other_col) 
select parent_id, 42 from parent_res


Since the Postgres IDENTITY (formerly known as SERIAL) columns are backed by SQL sequences, you can also use the LASTVAL() function to retrieve the most recently assigned identity (sequence) value in the session.