[jeltz]

PosttgreSQL has only very limited implicit type conversion (e.g. only between different text types and between different integer types) so I presume that what you refer to is how single quoted SQL literals are untyped and their content will be parsed depending on e.g. what you try to insert them into.

    $ CREATE TABLE t (x int);
    CREATE TABLE
    $ INSERT INTO t (x) VALUES (42);
    INSERT 0 1
    $ INSERT INTO t (x) VALUES ('42');
    INSERT 0 1
    $ INSERT INTO t (x) VALUES (CAST('42' AS text));
    ERROR:  column "x" is of type integer but expression is of type text
    LINE 1: INSERT INTO t (x) VALUES (CAST('42' AS text));
                                           ^
    HINT:  You will need to rewrite or cast the expression.
    $ INSERT INTO t (x) VALUES ('42a');
    ERROR:  invalid input syntax for type integer: "42a"
    LINE 1: INSERT INTO t (x) VALUES ('42a');

    $ INSERT INTO t (x) VALUES (CAST(42 AS bigint));
    INSERT 0 1