The DECIMAL datatype is a datatype in MySQL that provides additional precision over FLOATs or DOUBLEs at the expense of arithmetic. You specify the precision by using
datatype-name DECIMAL
or
datatype-name DECIMAL(8)
or
datatype-name DECIMAL(10,4)

MySQL uses roughly 4 bytes for every 9 digits either side of the decimal.

The english definition (http://www.thefreedictionary.com/decimal) would assume that when you specify the DECIMAL datatype you would want to insert numbers with fractions.

This however is not the case. Lets show this:

mysql> create database decimal_madness;
Query OK, 1 row affected (0.00 sec)

mysql> use decimal_madness;
Database changed
mysql> create table test1 ( tmp decimal);
Query OK, 0 rows affected (0.10 sec)

mysql> insert into test1 values(1.1);
Query OK, 1 …

Numeric types in MySQL have two varieties: - “precise” types such as INTEGER and DECIMAL; - the IEEE-standard floating point types FLOAT and DOUBLE. As a rule of thumb, the first group are for exact, “counted” quantities. The INTEGER types represent whole numbers, and DECIMAL represents “fixed point” decimal, with a preset number of places after the decimal point. Various widths of INTEGER are available in MySQL, from 8-bit TINYINT to 64-bit BIGINT. Calculations with integer types are fast, as they usually correspond to hardware register sizes. DECIMAL is commonly used for quantities like decimal currency where the number of digits of precision is known and fixed. For example, exactly counting pennies in two decimal digits. Computation with DECIMAL is slower than other types, but this is unlikely to impact most applications. In the other category are FLOAT and DOUBLE, which are the 32 and 64-bit IEEE standard types, which are usually …