Combine two tables into a new one so that select rows from the other one are ignored

Question

I have two tables that have identical columns. I would like to join these two tables together into a third one that contains all the rows from the first one and from the sec

Answer 1

UNION simply doesn't do what you describe. This query should:

CREATE TABLE AS 
SELECT date, location_code, product_code, quantity
FROM   transactions_kitchen k

UNION  ALL
SELECT h.date, h.location_code, h.product_code, h.quantity
FROM   transactions_admin h
LEFT   JOIN transactions_kitchen k USING (location_code, date)
WHERE  k.location_code IS NULL;

LEFT JOIN / IS NULL to exclude rows from the second table for the same location and date. See:

• Select rows which are not present in other table

Use CREATE TABLE AS instead of SELECT INTO. The manual:

CREATE TABLE AS is functionally similar to SELECT INTO. CREATE TABLE AS is the recommended syntax, since this form of SELECT INTO is not available in ECPG or PL/pgSQL, because they interpret the INTO clause differently. Furthermore, CREATE TABLE AS offers a superset of the functionality provided by SELECT INTO.

Or, if the target table already exists:

INSERT INTO transactions_combined ()
SELECT ...

Aside: I would not use date as column name. It's a reserved word in every SQL standard and a function and data type name in Postgres.