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

A normal-size (double-precision) floating-point number. Allowable
values are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0, and
2.2250738585072014E-308 to 1.7976931348623157E+308. These are the
theoretical limits, based on the IEEE standard. The actual range might
be slightly smaller depending on your hardware or operating system.

M is the total number of digits and D is the number of digits following
the decimal point. If M and D are omitted, values are stored to the
limits allowed by the hardware. A double-precision floating-point
number is accurate to approximately 15 decimal places.

UNSIGNED, if specified, disallows negative values.

URL: http://dev.mysql.com/doc/refman/5.1/en/numeric-type-overview.html

