Why does TINYINT(1) function as a boolean but INT(1) does not?

Question

Why does TINYINT(1) work as a boolean? The way I understood the official docs, the (1) should mean it has a display width of 1, so if I store 56 in

Answer 1

TINYINT columns can store numbers from -128 to 127.

TINYINT(1) is a bit weird though. It is (perhaps because it is supposed to act as a BOOLEAN datatype), returns only 0 and 1 in some context, while it still keeps the stored (-128 to 127) values.

(Correction: I only see this weird behaviour in SQL-Fiddle and not when accessing MySQL locally so it may well be a SQL-Fiddle quirkiness, possibly related to the quivalence with BOOLEAN) and not a MySQL problem.

See the SQL-Fiddle

CREATE TABLE test
( i TINYINT(1)
) ;

INSERT INTO test 
  (i)
VALUES
  (0),  (1), (6), (120), (-1) ;

Where we get (only in SQL-Fiddle, not if we access MySQL otherwise!):

SELECT i
FROM test ;

  i
-----
  0
  1
  1
  1
  1

but:

SELECT CAST(i AS SIGNED) i2
FROM test ;

  i2
-----
   0
   1
   6
 120
  -1