pg_enumThe pg_enum catalog contains
entries showing the values and labels for each enum type. The
internal representation of a given enum value is actually the OID
of its associated row in pg_enum.
Table 51.20. pg_enum Columns
| Name | Type | References | Description |
|---|---|---|---|
oid |
oid |
Row identifier (hidden attribute; must be explicitly selected) | |
enumtypid |
oid |
|
The OID of the pg_type entry
owning this enum value |
enumsortorder |
float4 |
The sort position of this enum value within its enum type | |
enumlabel |
name |
The textual label for this enum value |
The OIDs for pg_enum rows follow
a special rule: even-numbered OIDs are guaranteed to be ordered in
the same way as the sort ordering of their enum type. That is, if
two even OIDs belong to the same enum type, the smaller OID must
have the smaller enumsortorder
value. Odd-numbered OID values need bear no relationship to the
sort order. This rule allows the enum comparison routines to avoid
catalog lookups in many common cases. The routines that create and
alter enum types attempt to assign even OIDs to enum values
whenever possible.
When an enum type is created, its members are assigned
sort-order positions 1..n. But members added later might be
given negative or fractional values of enumsortorder. The only requirement on these
values is that they be correctly ordered and unique within each
enum type.
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