|
|
|
|
| |
The order of values in an ENUM declaration is the order used for sorting. The order of values in a SET declaration also determines sort order, although the relationship is more complicated because column values can contain multiple set members.
The order of values in a SET declaration determines the order in which set members appear when SET column values consisting of multiple members are displayed.
ENUM and SET are classified as string types because enumeration and set members are specified as strings when you create columns of these types. However, the members are stored internally as numbers and you can operate on them as such. This means that ENUM and SET types are more efficient than other string types because they often can be handled using numeric operations rather than string operations. It also means that ENUM and SET values can be used in either string or numeric contexts.
ENUM members in the column declaration are numbered sequentially beginning with 1. (0 is reserved by MySQL for the error member, which is represented in string form by the empty string.) The number of enumeration values determines the storage size of an ENUM column. One byte can represent 256 values, two bytes can represent 65,536 values. (Compare this to the ranges of the one-byte and two-byte integer types TINYINT UNSIGNED and SMALLINT UNSIGNED.) Thus, the maximum number of enumeration members is 65,536 (counting the error member) and the storage size depends on whether or not there are more than 256 members. You can specify a maximum of 65,535 (not 65,536) members in the ENUM declaration because MySQL reserves a spot for the error member as an implicit member of every enumeration. When you assign an illegal value to an ENUM column, MySQL assigns the error member instead.
|
|
|
|
|
|
| Link Partners: Asia florist, Flowers to India, Hong kong flowers, Site submit, Cheap web hosting, China florist, Japan florist |
|
