DECIMAL[(M[,D])] [UNSIGNED] [ZEROFILL]

An unpacked fixed-point number. Behaves like a CHAR column; "unpacked"
means the number is stored as a string, using one character for each
digit of the value. M is the total number of digits and D is the number
of digits after the decimal point. The decimal point and (for negative
numbers) the `-' sign are not counted in M, although space for them is
reserved. If D is 0, values have no decimal point or fractional part.
The maximum range of DECIMAL values is the same as for DOUBLE, but the
actual range for a given DECIMAL column may be constrained by the
choice of M and D. If D is omitted, the default is 0. If M is omitted,
the default is 10.

UNSIGNED, if specified, disallows negative values.

Note: Before MySQL 3.23, the value of M must be large enough to include
the space needed for the sign and the decimal point characters.
