How to declare a variable in a postgresql query in sql language ? - Mailing list pgsql-novice

In MS SQL Server I can do this:

DECLARE @myvar INT 
SET @myvar = 5 
 
SELECT * 
FROM somewhere 
WHERE something = @myvar 

How do I do the same in PostgreSQL in sql language? According to the documentation are declared simply as "name type;", but this gives me a syntax error:

myvar INTEGER;