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.
M is the total number of digits.
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.
DOUBLE PRECISION[(M,D)] [UNSIGNED] [ZEROFILL], REAL[(M,D)] [UNSIGNED] [ZEROFILL] are synonyms for DOUBLE.
If the REAL_AS_FLOAT SQL mode is set, REAL is a synonym for FLOAT rather than DOUBLE.