NULL in a in UNION sql statement

Question

When I run the following query

with table_a as 
  (select '1' as column_name union select '2' union NULL)
select * from table_a;

I get:

Syntax error: unexpected 'NULL'.

Is there a way to insert the NULL as part of the SELECT above?

Answer 1

UNION requires SELECT

with table_a as 
  (select '1' as column_name union select '2' union  SELECT NULL)
select * from table_a;

It is also possible to use VALUES:

with table_a(column_name) as 
  (SELECT * FROM VALUES ('1'),('2'),(NULL))
select * from table_a;