How can I cast an int to a bit in MySQL 5.1?

Question

I am transitioning from SQL Server to MySQL 5.1 and seem to be tripped up trying to create a table using a select statement so that the column is a bit.

Ideally the following would work:

CREATE TABLE myNewTable AS
SELECT cast(myIntThatIsZeroOrOne as bit) AS myBit
FROM myOldtable

However sql is very unhappy at casting as a bit. How can I tell it to select an int column (which I know only has 0s and 1s) as a bit?

Answer 1

You cannot!

CAST and CONVERT only work to:

• BINARY[(N)]
• CHAR[(N)]
• DATE
• DATETIME
• DECIMAL[(M[,D])]
• SIGNED [INTEGER]
• TIME
• UNSIGNED [INTEGER]

No room for: BIT, BITINT, TINYINT, MEDIUMINT, BIGINT, SMALLINT, ...

However, you can create your own function cast_to_bit(n):

DELIMITER $$

CREATE FUNCTION cast_to_bit (N INT) RETURNS bit(1)
BEGIN
    RETURN N;
END

To try it yourself, you can create view with several conversions like:

CREATE VIEW view_bit AS
    SELECT
        cast_to_bit(0),
        cast_to_bit(1),
        cast_to_bit(FALSE),
        cast_to_bit(TRUE),
        cast_to_bit(b'0'),
        cast_to_bit(b'1'),
        cast_to_bit(2=3),
        cast_to_bit(2=2)

... and then describe it!

DESCRIBE view_bit;

Ta-dah!! Everyone is bit(1) now!!!

Answer 2

Try CONV(N,from_base,to_base)

Converts numbers between different number bases. Returns a string representation of the number N, converted from base from_base to base to_base. Returns NULL if any argument is NULL. The argument N is interpreted as an integer, but may be specified as an integer or a string. The minimum base is 2 and the maximum base is 36. If to_base is a negative number, N is regarded as a signed number. Otherwise, N is treated as unsigned. CONV() works with 64-bit precision.

for example.

select CONV(9, 10, 2);

Answer 3

Try specifying a length for the bit data type.

CREATE TABLE myNewTable AS
SELECT cast(myIntThatIsZeroOrOne as bit(1)) AS myBit
FROM myOldtable

Answer 4

Try using case:

CREATE TABLE myNewTable AS
SELECT (case myIntThatIsZeroOrOne when 1 then true else false end) AS myBit
FROM myOldtable