sql - Difference between JOIN and INNER JOIN

As the other answers already state there is no difference in your example.

The relevant bit of grammar is documented here

 ::= 

    [ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [  ] ]
    JOIN

Showing that all are optional. The page further clarifies that

INNER Specifies all matching pairs of rows are returned. Discards
unmatched rows from both tables. When no join type is specified, this
is the default.

The grammar does also indicate that there is one time where the INNER is required though. When specifying a join hint.

See the example below

CREATE TABLE T1(X INT);
CREATE TABLE T2(Y INT);

SELECT *

FROM   T1
       LOOP JOIN T2
         ON X = Y;

SELECT *
FROM   T1
       INNER LOOP JOIN T2
         ON X = Y;