Source code editor What Is Ajax

↑

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`

. For numeric type storage requirements, see Section 11.5, “Data Type Storage Requirements”.

As of MySQL 5.0.3, a `BIT`

data type is available for storing bit-field values. (Before 5.0.3, MySQL interprets `BIT`

as `TINYINT(1)`

.) In MySQL 5.0.3, `BIT`

is supported only for `MyISAM`

. MySQL 5.0.5 extends `BIT`

support to `MEMORY`

, `InnoDB`

, and `BDB`

.

As an extension to the SQL standard, MySQL also supports the integer types `TINYINT`

, `MEDIUMINT`

, and `BIGINT`

. The following table shows the required storage and range for each of the integer types.

Type | Bytes | Minimum Value | Maximum Value |

(Signed/Unsigned) | (Signed/Unsigned) | ||

`TINYINT` | 1 | `-128` | `127` |

`0` | `255` | ||

`SMALLINT` | 2 | `-32768` | `32767` |

`0` | `65535` | ||

`MEDIUMINT` | 3 | `-8388608` | `8388607` |

`0` | `16777215` | ||

`INT` | 4 | `-2147483648` | `2147483647` |

`0` | `4294967295` | ||

`BIGINT` | 8 | `-9223372036854775808` | `9223372036854775807` |

`0` | `18446744073709551615` |

Another extension is supported by MySQL for optionally specifying the display width of integer data types in parentheses following the base keyword for the type (for example, `INT(4)`

). This optional display width is used to display integer values having a width less than the width specified for the column by left-padding them with spaces.

The display width does *not* constrain the range of values that can be stored in the column, nor the number of digits that are displayed for values having a width exceeding that specified for the column. For example, a column specified as `SMALLINT(3)`

has the usual `SMALLINT`

range of `-32768`

to `32767`

, and values outside the range allowed by three characters are displayed using more than three characters.

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 assumes that the data fits into the original column width.

**Note**: The `ZEROFILL`

attribute is stripped when a column is involved in expressions or `UNION`

queries.

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 larger upper numeric range for the column. For example, if an `INT`

column is `UNSIGNED`

, the size of the column's range is the same but its endpoints shift from `-2147483648`

and `2147483647`

up to `0`

and `4294967295`

.

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.

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

The `FLOAT`

and `DOUBLE`

data types are used to represent approximate numeric data values. For `FLOAT`

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. MySQL 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 a four-byte single-precision `FLOAT`

column. A precision from 24 to 53 results in an eight-byte double-precision `DOUBLE`

column.

MySQL allows a non-standard syntax: `FLOAT(`

or * M*,

`D`

`REAL(``M`

,`D`

)

or `DOUBLE PRECISION(``M`

,`D`

)

. Here, “`(``M`

,`D`

)

” means than values can be stored with up to `M`

`D`

`FLOAT(7,4)`

will look like `-999.9999`

when displayed. MySQL performs rounding when storing values, so if you insert `999.00009`

into a `FLOAT(7,4)`

column, the approximate result is `999.0001`

. MySQL treats `DOUBLE`

as a synonym for `DOUBLE PRECISION`

(a non-standard extension). MySQL also treats `REAL`

as a synonym for `DOUBLE PRECISION`

(a non-standard variation), unless the `REAL_AS_FLOAT`

SQL mode is enabled.

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 digits.

The `DECIMAL`

and `NUMERIC`

data types are used to store exact numeric data values. In MySQL, `NUMERIC`

is implemented as `DECIMAL`

. These types are used to store values for which it is important to preserve exact precision, for example with monetary data.

As of MySQL 5.0.3, `DECIMAL`

and `NUMERIC`

values are stored in binary format. Previously, they were stored as strings, with one character used for each digit of the value, the decimal point (if the scale is greater than 0), and the ‘`-`

’ sign (for negative numbers). See Chapter 21, *Precision Math*.

When declaring a `DECIMAL`

or `NUMERIC`

column, 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. 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 enforces this limit as of MySQL 5.0.3. Before 5.0.3, on the positive end of the range, the column could actually store numbers up to `9999.99`

. (For positive numbers, MySQL 5.0.2 and earlier used the byte reserved for the sign to extend the upper end of the range.)

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 allowed to decide the value of `M`

`DECIMAL`

and `NUMERIC`

syntax. The default value of `M`

The maximum number of digits for `DECIMAL`

or `NUMERIC`

is 65 (64 from MySQL 5.0.3 to 5.0.5). Before MySQL 5.0.3, 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.)

As of MySQL 5.0.3, the `BIT`

data type is used to store bit-field values. A type of `BIT(`

allows for storage of * M*)

`M`

`M`

To specify bit values, `b'`

notation can be used. * value*'

`value`

`b'111'`

and `b'10000000'`

represent 7 and 128, respectively. See Section 9.1.5, “Bit-Field Values”. If you assign a value to a `BIT(`

column that is less than * M*)

`M`

`b'101'`

to a `BIT(6)`

column is, in effect, the same as assigning `b'000101'`

. When asked to store a value in a numeric column that is outside the data type's allowable range, MySQL's behavior depends on the SQL mode in effect at the time. For example, if no restrictive modes are enabled, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead. However, if the mode is set to `TRADITIONAL`

, MySQL rejects a value that is out of range with an error, and the insert fails, in accordance with the SQL standard.

In non-strict mode, when an out-of-range value is assigned to an integer column, MySQL stores the value representing the corresponding endpoint of the column data type range. If you store 256 into a `TINYINT`

or `TINYINT UNSIGNED`

column, MySQL stores 127 or 255, respectively. When a floating-point or fixed-point 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 endpoint of that range.

Conversions that occur due to clipping when MySQL is not operating in strict mode are reported as warnings for `ALTER TABLE`

, `LOAD DATA INFILE`

, `UPDATE`

, and multiple-row `INSERT`

statements. When MySQL is operating in strict mode, these statements fail, and some or all of the values will not be inserted or changed, depending on whether the table is a transactional table and other factors. For details, see Section 5.2.6, “SQL Modes”.