SQL DECIMAL

DECIMAL(M,D)

Copy
 PRECISION (M)
/         \
1234567.123
        \ /
       SCALE (D)

M is the maximum number of digits (the precision). It has a range of 1 to 65. (Older versions of MySQL permitted a range of 1 to 254.)

D is the number of digits to the right of the decimal point (the scale). It has a range of 0 to 30 and must be no larger than M.

E.g.

DECIMAL(10,3) => 1234567.123

or in Rails speak

t.decimal :mycolumn, precision: 10, scale: 3 #=> 1234567.123

Confusingly number_to_percentage takes :precision option which specifies scale in the SQL speak.