The simplest concat in PostgreSQL does not want to be executed, what should I do?

Question

PostgreSQL

My whole brain has already broken, I can’t understand why the simplest concat () does not work in PosgreSql, even direct examples from reference books do not work. Maybe a problem with the database server? PostgreSQL version 8.4.20
SELECT CONCAT('Postgre', 'SQL');
Gives an error:

ОШИБКА:  функция concat(unknown, unknown) не существует
LINE 1: SELECT CONCAT('Postgre', 'SQL');
               ^
HINT:  Функция с данными именем и типами аргументов не найдена. Возможно, вам следует добавить явные преобразования типов.

Transforms don't help. These queries give the same result:

SELECT CONCAT(CAST('Postgre' as varchar), CAST('SQL' as varchar) );
SELECT CONCAT('Postgre'::text, 'SQL'::text );

Answer 1

RTFM
There is no concat() function in version 8.4. String concatenation is done with the ||