MySQL in a Nutshell, 2nd Edition

Name

DEC, DECIMAL, FIXED, NUMERIC

Synopsis

DECIMAL[(width[, decimals])] [UNSIGNED] [ZEROFILL]

This data column type is similar to FLOAT, but it’s used for accurate, fixed-point numbers. When calculating with a DECIMAL column, it has a 65-digit level of precision. The width given is the maximum width of the total digits—on both sides of the decimal place, not including the decimal point or the negative sign if a negative number. The decimals given are the number of decimals allowed and the number for which it zero-fills. For example, a column type setting of DECIMAL(4,2) that is given a value of 123.4 will return a warning and store the value as 99.99, the maximum amount given the width. If the same column is given a value of 12.3, it won’t generate any warnings and will store the value as 12.30. If UNSIGNED is used with DECIMAL, negative values are not allowed.

MySQL stores numbers in DECIMAL columns as strings. Therefore, numbers outside the maximum numeric range for this data type may be stored in a DECIMAL column. This data type may be retrieved and displayed as a string, but in a numeric context (i.e., as part of a calculation), it cannot exceed the values shown in the table.