For enum types (described in
Section 8.7
),
there are several functions that allow cleaner programming without
hard-coding particular values of an enum type.
These are listed in
Table 9.33
. The examples
assume an enum type created as:
CREATE TYPE rainbow AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'purple');
Table 9.33. Enum Support Functions
Function
Description
Example
Example Result
enum_first(anyenum)
Returns the first value of the input enum type
enum_first(null::rainbow)
red
enum_last(anyenum)
Returns the last value of the input enum type
enum_last(null::rainbow)
purple
enum_range(anyenum)
Returns all values of the input enum type in an ordered array
enum_range(null::rainbow)
{red,orange,yellow,green,blue,purple}
enum_range(anyenum, anyenum)
Returns the range between the two given enum values, as an ordered
array. The values must be from the same enum type. If the first
parameter is null, the result will start with the first value of
the enum type.
If the second parameter is null, the result will end with the last
value of the enum type.
enum_range('orange'::rainbow, 'green'::rainbow)
{orange,yellow,green}
enum_range(NULL, 'green'::rainbow)
{red,orange,yellow,green}
enum_range('orange'::rainbow, NULL)
{orange,yellow,green,blue,purple}
Notice that except for the two-argument form of
enum_range
,
these functions disregard the specific value passed to them; they care
only about its declared data type. Either null or a specific value of
the type can be passed, with the same result. It is more common to
apply these functions to a table column or function argument than to
a hardwired type name as suggested by the examples.