1CREATE DOMAIN(7) PostgreSQL 9.2.24 Documentation CREATE DOMAIN(7)
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6 CREATE_DOMAIN - define a new domain
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9 CREATE DOMAIN name [ AS ] data_type
10 [ COLLATE collation ]
11 [ DEFAULT expression ]
12 [ constraint [ ... ] ]
13 where constraint is:
15 [ CONSTRAINT constraint_name ]
17 { NOT NULL | NULL | CHECK (expression) }
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20 CREATE DOMAIN creates a new domain. A domain is essentially a data type
21 with optional constraints (restrictions on the allowed set of values).
22 The user who defines a domain becomes its owner.
23 If a schema name is given (for example, CREATE DOMAIN myschema.mydomain
25 ...) then the domain is created in the specified schema. Otherwise it
26 is created in the current schema. The domain name must be unique among
27 the types and domains existing in its schema.
28 Domains are useful for abstracting common constraints on fields into a
30 single location for maintenance. For example, several tables might
31 contain email address columns, all requiring the same CHECK constraint
32 to verify the address syntax. Define a domain rather than setting up
33 each table's constraint individually.
34 To be able to create a domain, you must have USAGE privilege on the
36 underlying type.
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39 name
40 The name (optionally schema-qualified) of a domain to be created.
41 data_type
43 The underlying data type of the domain. This can include array
44 specifiers.
45 collation
47 An optional collation for the domain. If no collation is specified,
48 the underlying data type's default collation is used. The
49 underlying type must be collatable if COLLATE is specified.
50 DEFAULT expression
52 The DEFAULT clause specifies a default value for columns of the
53 domain data type. The value is any variable-free expression (but
54 subqueries are not allowed). The data type of the default
55 expression must match the data type of the domain. If no default
56 value is specified, then the default value is the null value.
57 The default expression will be used in any insert operation that
59 does not specify a value for the column. If a default value is
60 defined for a particular column, it overrides any default
61 associated with the domain. In turn, the domain default overrides
62 any default value associated with the underlying data type.
63 CONSTRAINT constraint_name
65 An optional name for a constraint. If not specified, the system
66 generates a name.
67 NOT NULL
69 Values of this domain are normally prevented from being null.
70 However, it is still possible for a domain with this constraint to
71 take a null value if it is assigned a matching domain type that has
72 become null, e.g. via a LEFT OUTER JOIN, or INSERT INTO tab
73 (domcol) VALUES ((SELECT domcol FROM tab WHERE false)).
74 NULL
76 Values of this domain are allowed to be null. This is the default.
77 This clause is only intended for compatibility with nonstandard SQL
79 databases. Its use is discouraged in new applications.
80 CHECK (expression)
82 CHECK clauses specify integrity constraints or tests which values
83 of the domain must satisfy. Each constraint must be an expression
84 producing a Boolean result. It should use the key word VALUE to
85 refer to the value being tested.
86 Currently, CHECK expressions cannot contain subqueries nor refer to
88 variables other than VALUE.
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91 This example creates the us_postal_code data type and then uses the
92 type in a table definition. A regular expression test is used to verify
93 that the value looks like a valid US postal code:
94 CREATE DOMAIN us_postal_code AS TEXT
96 CHECK(
97 VALUE ~ '^\d{5}$'
98 OR VALUE ~ '^\d{5}-\d{4}$'
99 );
100 CREATE TABLE us_snail_addy (
102 address_id SERIAL PRIMARY KEY,
103 street1 TEXT NOT NULL,
104 street2 TEXT,
105 street3 TEXT,
106 city TEXT NOT NULL,
107 postal us_postal_code NOT NULL
108 );
109
111 The command CREATE DOMAIN conforms to the SQL standard.
112
114 ALTER DOMAIN (ALTER_DOMAIN(7)), DROP DOMAIN (DROP_DOMAIN(7))
115PostgreSQL 9.2.24 2017-11-06 CREATE DOMAIN(7)