Subquery in SELECT statement returns wrong(?) data type (no replies)

Hi,

I am having an issue with a subquery in SELECT statement returning unexpected data type.

Consider the following example:

CREATE TABLE foo (
id INT(11) NOT NULL AUTO_INCREMENT,
a BIT(1) NOT NULL,
PRIMARY KEY (id)
)
ENGINE=InnoDB;

CREATE TABLE bar (
id INT(11) NOT NULL AUTO_INCREMENT,
b BIT(1) NULL,
PRIMARY KEY (id)
)
ENGINE=InnoDB;

CREATE TEMPORARY TABLE temp
SELECT foo.a AS result_a, (SELECT bar.b FROM bar WHERE bar.id = foo.id LIMIT 1) AS result_b
FROM foo
LIMIT 0;
DESCRIBE temp;

+----------+-----------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-----------------+------+-----+---------+-------+
| result_a | bit(1) | NO | | NULL | |
| result_b | int(1) unsigned | YES | | NULL | |
+----------+-----------------+------+-----+---------+-------+


As can be seen from the output, result_b is an unsigned integer instead of an expected(?) BIT(1).

Generaly this wouldn't be an issue. However, since we are using Entity Framework which doesn't like mapping unsigned integers to 'bool' properties, this brings all sorts of problems. Basically bar.b is always mapped to 'true' on the code level no matter of the actual underlying value.


My question though is not about the EF, but rather why the returned datatype doesn't match the original one? Is this an expected behaviour?


As a workaround, we solved this simply by casting to a signed integer CAST(bar.b AS SIGNED INTEGER) [I suppose IF(bar.b=0,0,1) should work too].