MySQL supports all of the standard SQL numeric data types. These types include the exact numeric data types (INTEGER, SMALLINT, DECIMAL, and NUMERIC), as well as the approximate numeric data types (FLOAT, REAL, and DOUBLE PRECISION). The keyword INT is a synonym for INTEGER, and the keyword DEC is a synonym for DECIMAL.

As an extension to the SQL standard, MySQL also supports the integer types TINYINT, MEDIUMINT, and BIGINT as listed in the following table.

Another extension is supported by MySQL for optionally specifying the display width of an integer value in parentheses following the base keyword for the type (for example, INT(4)). This optional display width specification is used to left-pad the display of values having a width less than the width specified for the column.

The display width does not constrain the range of values that can be stored in the column, nor the number of digits that will be displayed for values having a width exceeding that specified for the column.

When used in conjunction with the optional extension attribute ZEROFILL, the default padding of spaces is replaced with zeros. For example, for a column declared as INT(5) ZEROFILL, a value of 4 is retrieved as 00004. Note that if you store larger values than the display width in an integer column, you may experience problems when MySQL generates temporary tables for some complicated joins, because in these cases MySQL trusts that the data did fit into the original column width.

All integer types can have an optional (non-standard) attribute UNSIGNED. Unsigned values can be used when you want to allow only non-negative numbers in a column and you need a bigger upper numeric range for the column.

As of MySQL 4.0.2, floating-point and fixed-point types also can be UNSIGNED. As with integer types, this attribute prevents negative values from being stored in the column. However, unlike the integer types, the upper range of column values remains the same.

If you specify ZEROFILL for a numeric column, MySQL automatically adds the UNSIGNED attribute to the column.

The DECIMAL and NUMERIC types are implemented as the same type by MySQL. They are used to store values for which it is important to preserve exact precision, for example with monetary data. When declaring a column of one of these types, 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 decimal digits that will be stored for values, and the scale represents the number of digits that will be stored following the decimal point.

MySQL stores DECIMAL and NUMERIC values as strings, rather than as binary floating-point numbers, in order to preserve the decimal precision of those values. One character is used for each digit of the value, the decimal point (if the scale is greater than 0), and the ‘-’ sign (for negative numbers). If the scale is 0, DECIMAL and NUMERIC values contain no decimal point or fractional part.

Standard SQL requires that the salary column be able to store any value with five digits and two decimals. In this case, therefore, the range of values that can be stored in the salary column is from -999.99 to 999.99. MySQL varies from this in two ways:

In standard SQL, the syntax DECIMAL(M) is equivalent to DECIMAL(M,0). Similarly, the syntax DECIMAL is equivalent to DECIMAL(M,0), where the implementation is allowed to decide the value of M. As of MySQL 3.23.6, both of these variant forms of the DECIMAL and NUMERIC data types are supported. The default value of M is 10. Before 3.23.6, M and D both must be specified explicitly.

The maximum range of DECIMAL and NUMERIC values is the same as for DOUBLE, but the actual range for a given DECIMAL or NUMERIC 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 allowed 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 allowable number of digits.) When a DECIMAL or NUMERIC column is assigned a value that exceeds the range implied by the specified (or default) precision and scale, MySQL stores the value representing the corresponding end point of that range.

For floating-point column types, MySQL uses four bytes for single-precision values and eight bytes for double-precision values.

The FLOAT type is used to represent approximate numeric data types. The SQL standard allows an optional specification of the precision (but not the range of the exponent) in bits following the keyword FLOAT in parentheses. The MySQL implementation also supports this optional precision specification, but the precision value is used only to determine storage size. A precision from 0 to 23 results in four-byte single-precision FLOAT column. A precision from 24 to 53 results in eight-byte double-precision DOUBLE column.

When the keyword FLOAT is used for a column type without a precision specification, MySQL uses four bytes to store the values. MySQL also supports variant syntax with two numbers given in parentheses following the FLOAT keyword. The first number represents the display width and the second number specifies the number of digits to be stored and displayed following the decimal point (as with DECIMAL and NUMERIC). When MySQL is asked to store a number for such a column with more decimal digits following the decimal point than specified for the column, the value is rounded to eliminate the extra digits when the value is stored.

In standard SQL, the REAL and DOUBLE PRECISION types do not accept precision specifications. MySQL supports a variant syntax with two numbers given in parentheses following the type name. The first number represents the display width and the second number specifies the number of digits to be stored and displayed following the decimal point. As an extension to the SQL standard, MySQL recognizes DOUBLE as a synonym for the DOUBLE PRECISION type. In contrast with the standard's requirement that the precision for REAL be smaller than that used for DOUBLE PRECISION, MySQL implements both as eight-byte double-precision floating-point values (unless the server SQL mode includes the REAL_AS_FLOAT option).

For maximum portability, code requiring storage of approximate numeric data values should use FLOAT or DOUBLE PRECISION with no specification of precision or number of decimal points.

When asked to store a value in a numeric column that is outside the column type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.

For example, the range of an INT column is -2147483648 to 2147483647. If you try to insert -9999999999 into an INT column, MySQL clips the value to the lower endpoint of the range and stores -2147483648 instead. Similarly, if you try to insert 9999999999, MySQL clips the value to the upper endpoint of the range and stores 2147483647 instead.

If the INT column is UNSIGNED, the size of the column's range is the same but its endpoints shift up to 0 and 4294967295. If you try to store -9999999999 and 9999999999, the values stored in the column are 0 and 4294967296.

Conversions that occur due to clipping are reported as “warnings” for ALTER TABLE, LOAD DATA INFILE, UPDATE, and multiple-row INSERT statements.