1CREATE DOMAIN()                  SQL Commands                  CREATE DOMAIN()
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NAME

6       CREATE DOMAIN - define a new domain
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SYNOPSIS

10       CREATE DOMAIN name [ AS ] data_type
11           [ DEFAULT expression ]
12           [ constraint [ ... ] ]
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14       where constraint is:
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16       [ CONSTRAINT constraint_name ]
17       { NOT NULL | NULL | CHECK (expression) }
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DESCRIPTION

21       CREATE DOMAIN creates a new domain. A domain is essentially a data type
22       with optional constraints (restrictions on the allowed set of  values).
23       The user who defines a domain becomes its owner.
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25       If a schema name is given (for example, CREATE DOMAIN myschema.mydomain
26       ...) then the domain is created in the specified schema.  Otherwise  it
27       is created in the current schema.  The domain name must be unique among
28       the types and domains existing in its schema.
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30       Domains are useful for abstracting common constraints on fields into  a
31       single location for maintenance. For example, several tables might con‐
32       tain email address columns, all requiring the same CHECK constraint  to
33       verify the address syntax.  Define a domain rather than setting up each
34       table's constraint individually.
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PARAMETERS

37       name   The name (optionally schema-qualified) of a domain  to  be  cre‐
38              ated.
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40       data_type
41              The  underlying  data type of the domain. This may include array
42              specifiers.
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44       DEFAULT expression
45              The DEFAULT clause specifies a default value for columns of  the
46              domain data type. The value is any variable-free expression (but
47              subqueries are not allowed).   The  data  type  of  the  default
48              expression must match the data type of the domain. If no default
49              value is specified, then the default value is the null value.
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51              The default expression will be used in any insert operation that
52              does  not  specify a value for the column. If a default value is
53              defined for a particular column, it overrides any default  asso‐
54              ciated  with  the  domain. In turn, the domain default overrides
55              any default value associated with the underlying data type.
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57       CONSTRAINT constraint_name
58              An optional name for a constraint. If not specified, the  system
59              generates a name.
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61       NOT NULL
62              Values of this domain are not allowed to be null.
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64       NULL   Values  of  this  domain  are  allowed  to  be null. This is the
65              default.
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67              This clause is only intended for compatibility with  nonstandard
68              SQL databases. Its use is discouraged in new applications.
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70       CHECK (expression)
71              CHECK  clauses specify integrity constraints or tests which val‐
72              ues of the domain must satisfy.   Each  constraint  must  be  an
73              expression  producing  a  Boolean  result. It should use the key
74              word VALUE to refer to the value being tested.
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76              Currently, CHECK expressions cannot contain subqueries nor refer
77              to variables other than VALUE.
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EXAMPLES

80       This  example  creates  the  us_postal_code data type and then uses the
81       type in a table definition. A regular expression test is used to verify
82       that the value looks like a valid US postal code.
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84       CREATE DOMAIN us_postal_code AS TEXT
85       CHECK(
86          VALUE ~ '^\\d{5}$'
87       OR VALUE ~ '^\\d{5}-\\d{4}$'
88       );
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90       CREATE TABLE us_snail_addy (
91         address_id SERIAL PRIMARY KEY,
92         street1 TEXT NOT NULL,
93         street2 TEXT,
94         street3 TEXT,
95         city TEXT NOT NULL,
96         postal us_postal_code NOT NULL
97       );
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COMPATIBILITY

101       The command CREATE DOMAIN conforms to the SQL standard.
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SEE ALSO

104       ALTER DOMAIN [alter_domain(7)], DROP DOMAIN [drop_domain(l)]
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108SQL - Language Statements         2008-06-08                   CREATE DOMAIN()