Using the EXCEPT clause in PostgreSQL

Question

I am trying to use a clause EXCEPTto retrieve data from a table. I want to get all rows from table1except those that exist in table2. As far as I understand, the following will not work:

CREATE TABLE table1(pk_id int, fk_id_tbl2 int);
CREATE TABLE table2(pk_id int);

Select fk_id_tbl2
FROM table1
Except
Select pk_id
FROM table2

The only way I can use EXCEPTis to select from the same tables or select columns with the same column name from different tables.

Can someone explain how to use the explanation clause better?

Answer 1

Your query seems perfectly true:

SELECT fk_id_tbl2 AS some_name
FROM   table1
EXCEPT  -- you may want to use EXCEPT ALL
SELECT pk_id
FROM   table2;

Column names . . fk_id_tbl2, , SELECT. .

: EXCEPT ( ) EXCEPT ALL - . , :

• ,

EXCEPT .