CREATE [ [ LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name (
{ column_namedata_type [ DEFAULT default_expr ] [ column_constraint [, ... ] ]
| table_constraint } [, ... ]
)
[ INHERITS ( parent_table [, ... ] ) ]
[ WITH OIDS | WITHOUT OIDS ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | UNIQUE | PRIMARY KEY |
CHECK (expression) |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL ]
[ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint is:
[ CONSTRAINT constraint_name ]
{ UNIQUE ( column_name [, ... ] ) |
PRIMARY KEY ( column_name [, ... ] ) |
CHECK ( expression ) |
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL ] [ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
Description
CREATE TABLE will create a new, initially empty table
in the current database. The table will be owned by the user issuing the
command.
If a schema name is given (for example, CREATE TABLE
myschema.mytable ...) then the table is created in the
specified schema. Otherwise it is created in the current schema (the one
at the front of the search path; see CURRENT_SCHEMA()).
TEMP tables exist in a special schema, so a schema name may not be
given when creating a TEMP table.
The table name must be distinct from the name of any other table,
sequence, index, or view in the same schema.
CREATE TABLE also automatically creates a data
type that represents the tuple type (structure type) corresponding
to one row of the table. Therefore, tables cannot have the same
name as any existing data type in the same schema.
A table cannot have more than 1600 columns. (In practice, the
effective limit is lower because of tuple-length constraints).
The optional constraint clauses specify constraints (or tests) that
new or updated rows must satisfy for an insert or update operation
to succeed. A constraint is a named rule: an SQL object which
helps define valid sets of values by putting limits on the results
of insert, update, or delete operations performed on a table.
There are two ways to define constraints: table constraints and
column constraints. A column constraint is defined as part of a
column definition. A table constraint definition is not tied to a
particular column, and it can encompass more than one column.
Every column constraint can also be written as a table constraint;
a column constraint is only a notational convenience if the
constraint only affects one column.
Parameters
[LOCAL] TEMPORARY or [LOCAL] TEMP
If specified, the table is created as a temporary table.
Temporary tables are automatically dropped at the end of a
session. Existing permanent tables with the same name are not
visible to the current session while the temporary table exists,
unless they are referenced with schema-qualified names.
Any indexes created on a temporary table are automatically
temporary as well.
The LOCAL word is optional. But see under
Compatibility.
table_name
The name (optionally schema-qualified) of the table to be created.
column_name
The name of a column to be created in the new table.
data_type
The data type of the column. This may include array specifiers.
Refer to the User's Guide for further
information about data types and arrays.
DEFAULT
default_expr
The DEFAULT clause assigns a default data value for
the column whose column definition it appears within. The value
is any variable-free expression (subselects and cross-references
to other columns in the current table are not allowed). The
data type of the default expression must match the data type of the
column.
The default expression will be used in any insert operation that
does not specify a value for the column. If there is no default
for a column, then the default is NULL.
INHERITS ( parent_table [, ... ] )
The optional INHERITS clause specifies a list of
tables from which the new table automatically inherits all
columns. If the same column name exists in more than one parent
table, an error is reported unless the data types of the columns
match in each of the parent tables. If there is no conflict,
then the duplicate columns are merged to form a single column in
the new table. If the column name list of the new table
contains a column that is also inherited, the data type must
likewise match the inherited column(s), and the column
definitions are merged into one. However, inherited and new
column declarations of the same name need not specify identical
constraints: all constraints provided from any declaration are
merged together and all are applied to the new table. If the
new table explicitly specifies a default value for the column,
this default overrides any defaults from inherited declarations
of the column. Otherwise, any parents that specify default
values for the column must all specify the same default, or an
error will be reported.
WITH OIDS or WITHOUT OIDS
This optional clause specifies whether rows of the new table
should have OIDs (object identifiers) assigned to them. The
default is to have OIDs. (If the new table inherits from any
tables that have OIDs, then WITH OIDS is forced even
if the command says WITHOUT OIDS.)
Specifying WITHOUT OIDS allows the user to suppress
generation of OIDs for rows of a table. This may be worthwhile
for large tables, since it will reduce OID consumption and
thereby postpone wraparound of the 32-bit OID counter. Once the
counter wraps around, uniqueness of OIDs can no longer be
assumed, which considerably reduces their usefulness.
CONSTRAINT constraint_name
An optional name for a column or table constraint. If not specified,
the system generates a name.
NOT NULL
The column is not allowed to contain NULL values.
NULL
The column is allowed to contain NULL values. This is the default.
This clause is only available for compatibility with
non-standard SQL databases. Its use is discouraged in new
applications.
The UNIQUE constraint specifies a rule that a
group of one or more distinct columns of a table may contain
only unique values. The behavior of the unique table constraint
is the same as that for column constraints, with the additional
capability to span multiple columns.
For the purpose of a unique constraint, NULL values are not
considered equal.
Each unique table constraint must name a set of columns that is
different from the set of columns named by any other unique or
primary key constraint defined for the table. (Otherwise it
would just be the same constraint listed twice.)
The primary key constraint specifies that a column or columns of a table
may contain only unique (non-duplicate), non-NULL values.
Technically, PRIMARY KEY is merely a
combination of UNIQUE and NOT NULL, but
identifying a set of columns as primary key also provides
meta-data about the design of the schema, as a primary key
implies that other tables
may rely on this set of columns as a unique identifier for rows.
Only one primary key can be specified for a table, whether as a
column constraint or a table constraint.
The primary key constraint should name a set of columns that is
different from other sets of columns named by any unique
constraint defined for the same table.
CHECK (expression)
CHECK clauses specify integrity constraints or tests
which new or updated rows must satisfy for an insert or update
operation to succeed. Each constraint must be an expression
producing a Boolean result. A condition appearing within a
column definition should reference that column's value only,
while a condition appearing as a table constraint may reference
multiple columns.
Currently, CHECK expressions cannot contain
subselects nor refer to variables other than columns of the
current row.
REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] (column constraint) FOREIGN KEY ( column [, ... ] )
REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH matchtype ]
[ ON DELETE action ]
[ ON UPDATE action ]
(table constraint)
The REFERENCES column constraint specifies
that a group of one or more columns of the new table must only
contain values which match against values in the referenced
column(s) refcolumn
of the referenced table reftable. If refcolumn is omitted, the
primary key of the reftable is used. The
referenced columns must be the columns of a unique or primary
key constraint in the referenced table.
A value added to these columns is matched against the values of
the referenced table and referenced columns using the given
match type. There are three match types: MATCH
FULL, MATCH PARTIAL, and a default match type if
none is specified. MATCH FULL will not allow one
column of a multicolumn foreign key to be NULL unless all
foreign key columns are NULL. The default match type allows some
foreign key columns to be NULL while other parts of the foreign
key are not NULL. MATCH PARTIAL is not yet
implemented.
In addition, when the data in the referenced columns is changed,
certain actions are performed on the data in this table's
columns. The ON DELETE clause specifies the
action to do when a referenced row in the referenced table is
being deleted. Likewise, the ON UPDATE
clause specifies the action to perform when a referenced column
in the referenced table is being updated to a new value. If the
row is updated, but the referenced column is not actually
changed, no action is done. There are the following possible
actions for each clause:
NO ACTION
Produce an error indicating that the deletion or update
would create a foreign key constraint violation. This is
the default action.
RESTRICT
Same as NO ACTION.
CASCADE
Delete any rows referencing the deleted row, or update the
value of the referencing column to the new value of the
referenced column, respectively.
SET NULL
Set the referencing column values to NULL.
SET DEFAULT
Set the referencing column values to their default value.
If primary key column is updated frequently, it may be wise to
add an index to the REFERENCES column so that
NO ACTION and CASCADE
actions associated with the REFERENCES
column can be more efficiently performed.
DEFERRABLE or NOT DEFERRABLE
This controls whether the constraint can be deferred. A
constraint that is not deferrable will be checked immediately
after every command. Checking of constraints that are
deferrable may be postponed until the end of the transaction
(using the SET CONSTRAINTS command).
NOT DEFERRABLE is the default. Only foreign
key constraints currently accept this clause. All other
constraint types are not deferrable.
INITIALLY IMMEDIATE or INITIALLY DEFERRED
If a constraint is deferrable, this clause specifies the default
time to check the constraint. If the constraint is
INITIALLY IMMEDIATE, it is checked after each
statement. This is the default. If the constraint is
INITIALLY DEFERRED, it is checked only at the
end of the transaction. The constraint check time can be
altered with the SET CONSTRAINTS command.
Diagnostics
CREATE TABLE
Message returned if table is successfully created.
ERROR
Message returned if table creation failed. This is usually
accompanied by some descriptive text, such as:
ERROR: Relation 'table' already
exists, which occurs at run time if the table
specified already exists in the database.
Notes
Whenever an application makes use of OIDs to identify specific
rows of a table, it is recommended to create a unique constraint
on the oid column of that table, to ensure that
OIDs in the table will indeed uniquely identify rows even after
counter wraparound. Avoid assuming that OIDs are unique across
tables; if you need a database-wide unique identifier, use the
combination of tableoid and row OID for the
purpose. (It is likely that future PostgreSQL
releases will use a separate OID counter for each table, so that
it will be necessary, not optional, to include
tableoid to have a unique identifier
database-wide.)
Tip: The use of WITHOUT OIDS is not recommended
for tables with no primary key, since without either an OID or a
unique data key, it is difficult to identify specific rows.
PostgreSQL automatically creates an
index for each unique constraint and primary key constraint to
enforce the uniqueness. Thus, it is not necessary to create an
explicit index for primary key columns. (See CREATE INDEX for more information.)
The SQL92 standard says that CHECK column constraints
may only refer to the column they apply to; only
CHECK table constraints may refer to multiple
columns. PostgreSQL does not enforce
this restriction; it treats column and table check constraints
alike.
Unique constraints and primary keys are not inherited in the
current implementation. This makes the combination of
inheritance and unique constraints rather dysfunctional.
Examples
Create table films and table
distributors:
CREATE TABLE films (
code CHARACTER(5) CONSTRAINT firstkey PRIMARY KEY,
title CHARACTER VARYING(40) NOT NULL,
did DECIMAL(3) NOT NULL,
date_prod DATE,
kind CHAR(10),
len INTERVAL HOUR TO MINUTE
);
CREATE TABLE distributors (
did DECIMAL(3) PRIMARY KEY DEFAULT NEXTVAL('serial'),
name VARCHAR(40) NOT NULL CHECK (name <> '')
);
Create a table with a 2-dimensional array:
CREATE TABLE array (
vector INT[][]
);
Define a unique table constraint for the table films. Unique table
constraints can be defined on one or more columns of the table:
CREATE TABLE films (
code CHAR(5),
title VARCHAR(40),
did DECIMAL(3),
date_prod DATE,
kind VARCHAR(10),
len INTERVAL HOUR TO MINUTE,
CONSTRAINT production UNIQUE(date_prod)
);
Define a check column constraint:
CREATE TABLE distributors (
did DECIMAL(3) CHECK (did > 100),
name VARCHAR(40)
);
Define a check table constraint:
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40)
CONSTRAINT con1 CHECK (did > 100 AND name <> '')
);
Define a primary key table constraint for the table
films. Primary key table constraints can be defined
on one or more columns of the table.
CREATE TABLE films (
code CHAR(5),
title VARCHAR(40),
did DECIMAL(3),
date_prod DATE,
kind VARCHAR(10),
len INTERVAL HOUR TO MINUTE,
CONSTRAINT code_title PRIMARY KEY(code,title)
);
Define a primary key constraint for table
distributors. The following two examples are
equivalent, the first using the table constraint syntax, the second
the column constraint notation.
CREATE TABLE distributors (
did DECIMAL(3),
name CHAR VARYING(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did DECIMAL(3) PRIMARY KEY,
name VARCHAR(40)
);
This assigns a literal constant default value for the column
name, and arranges for the default value of
column did to be generated by selecting the next
value of a sequence object. The default value of
modtime will be the time at which the row is
inserted.
CREATE TABLE distributors (
name VARCHAR(40) DEFAULT 'luso films',
did INTEGER DEFAULT NEXTVAL('distributors_serial'),
modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
Define two NOT NULL column constraints on the table
distributors, one of which is explicitly
given a name:
CREATE TABLE distributors (
did DECIMAL(3) CONSTRAINT no_null NOT NULL,
name VARCHAR(40) NOT NULL
);
Define a unique constraint for the name column:
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40) UNIQUE
);
The above is equivalent to the following specified as a table constraint:
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40),
UNIQUE(name)
);
Compatibility
The CREATE TABLE conforms to SQL92 Intermediate
and to a subset of SQL99, with exceptions listed below and in the
descriptions above.
Temporary Tables
In addition to the local temporary table, SQL92 also defines a
CREATE GLOBAL TEMPORARY TABLE statement.
Global temporary tables are also visible to other sessions.
For temporary tables, there is an optional ON COMMIT clause:
CREATE { GLOBAL | LOCAL } TEMPORARY TABLE table ( ... ) [ ON COMMIT { DELETE | PRESERVE } ROWS ]
The ON COMMIT clause specifies whether or not
the temporary table should be emptied of rows whenever
COMMIT is executed. If the ON
COMMIT clause is omitted, SQL92 specifies that the default is
ON COMMIT DELETE ROWS. However, the behavior of
PostgreSQL is always like ON
COMMIT PRESERVE ROWS.
NULL"Constraint"
The NULL"constraint" (actually a
non-constraint) is a PostgreSQL
extension to SQL92 that is included for compatibility with some
other RDBMS (and for symmetry with the NOT
NULL constraint). Since it is the default for any
column, its presence is simply noise.
Assertions
An assertion is a special type of integrity constraint and shares
the same namespace as other constraints. However, an assertion is
not necessarily dependent on one particular table as constraints
are, so SQL92 provides the CREATE ASSERTION
statement as an alternate method for defining a constraint:
CREATE ASSERTION name CHECK ( condition )
PostgreSQL does not implement assertions at present.
Inheritance
Multiple inheritance via the INHERITS clause is
a PostgreSQL language extension. SQL99
(but not SQL92) defines single inheritance using a different
syntax and different semantics. SQL99-style inheritance is not
yet supported by PostgreSQL.
