MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6

The `DECIMAL`

and `NUMERIC`

types store exact numeric data values. These types are used when
it is important to preserve exact precision, for example with
monetary data. In MySQL, `NUMERIC`

is
implemented as `DECIMAL`

, so the following
remarks about `DECIMAL`

apply equally to
`NUMERIC`

.

MySQL stores `DECIMAL`

values in binary format.
See Section 12.22, “Precision Math”.

In a `DECIMAL`

column declaration, the
precision and scale can be (and usually is) specified; for
example:

salary DECIMAL(5,2)

In this example, `5`

is the precision and
`2`

is the scale. The precision represents the
number of significant digits that are stored for values, and the
scale represents the number of digits that can be stored
following the decimal point.

Standard SQL requires that `DECIMAL(5,2)`

be
able to store any value with five digits and two decimals, so
values that can be stored in the `salary`

column range from `-999.99`

to
`999.99`

.

In standard SQL, the syntax
`DECIMAL(`

is
equivalent to
* M*)

`DECIMAL(``M`

,0)

.
Similarly, the syntax `DECIMAL`

is equivalent
to `DECIMAL(``M`

,0)

,
where the implementation is permitted to decide the value of
`M`

`DECIMAL`

syntax. The default
value of `M`

If the scale is 0, `DECIMAL`

values contain no
decimal point or fractional part.

The maximum number of digits for `DECIMAL`

is
65, but the actual range for a given `DECIMAL`

column can be constrained by the precision or scale for a given
column. When such a column is assigned a value with more digits
following the decimal point than are permitted by the specified
scale, the value is converted to that scale. (The precise
behavior is operating system-specific, but generally the effect
is truncation to the permissible number of digits.)