Comment by randomdata

That is strong typing. Python, a dynamically typed language, exhibits the same quality:

    >>> v = ""
    >>> v + 42
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: can only concatenate str (not "int") to str

Types are most certainly not static (at least not in Postgres or most other implementations):

    CREATE TABLE varchars(v VARCHAR);
    ALTER TABLE varchars ALTER COLUMN v TYPE INTEGER USING v::integer;
    PREPARE v1 AS SELECT v + 42 FROM varchars;