INSERT in single query into 2 tables postgresql

Question

I have this 3 tables.

Employee
PK : id
name

completedBy
FK : employee_id
FK : order_id

Order
PK : id
date

I created form for creating order w

Answer 1

This can be done using a data modifying common table expression:

with new_order as (
  insert into orders (id, date) values (1, current_date)
  returning id
)
insert into completedby (employee_id, order_id)
values 
( 42 -- employee_id, 
  (select id from new_order)
);

The first part inserts into the orders table and returns the ID that was inserted. The second part then inserts the row into the completedby table using the known employee_id and retrieving the order_id from the previous step.

Edit

if the id column in the orders table is a serial column and you want to let the sequence generate the value you can do that as well:

with new_order as (
  insert into orders (date) values (current_date)
  returning id
)
insert into completedby (employee_id, order_id)
values 
( 42 -- employee_id, 
  (select id from new_order)
);