create_table manpage
CREATE TABLE() SQL Commands CREATE TABLE()
NAME
CREATE TABLE - define a new table
SYNOPSIS
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name ( [
{ column_name data_type [ DEFAULT default_expr ] [ column_constraint [ ... ] ]
| table_constraint
| LIKE parent_table [ { INCLUDING | EXCLUDING } DEFAULTS ] }
[, ... ]
] )
[ INHERITS ( parent_table [, ... ] ) ]
[ WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL |
NULL |
UNIQUE [ USING INDEX TABLESPACE tablespace ] |
PRIMARY KEY [ USING INDEX TABLESPACE tablespace ] |
CHECK (expression) |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint is:
[ CONSTRAINT constraint_name ]
{ UNIQUE ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] |
PRIMARY KEY ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] |
CHECK ( expression ) |
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ 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. Temporary tables exist in a special
schema, so a schema name may not be given when creating a temporary ta-
ble. The name of the table 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
composite type corresponding to one row of the table. Therefore, tables
cannot have the same name as any existing data type in the same schema.
The optional constraint clauses specify constraints (tests) that new or
updated rows must satisfy for an insert or update operation to succeed.
A constraint is an SQL object that helps define the set of valid values
in the table in various ways.
There are two ways to define constraints: table constraints and column
constraints. A column constraint is defined as part of a column defini-
tion. 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 for use when the constraint only affects one
column.
PARAMETERS
TEMPORARY or TEMP
If specified, the table is created as a temporary table. Tempo-
rary tables are automatically dropped at the end of a session,
or optionally at the end of the current transaction (see ON COM-
MIT below). 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.
Optionally, GLOBAL or LOCAL can be written before TEMPORARY or
TEMP. This makes no difference in PostgreSQL, but see Compati-
bility [create_table(7)].
table_name
The name (optionally schema-qualified) of the table to be cre-
ated.
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.
For more information on the data types supported by PostgreSQL,
refer to the documentation.
DEFAULT
The DEFAULT clause assigns a default data value for the column
whose column definition it appears within. The value is any
variable-free expression (subqueries 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.
Use of INHERITS creates a persistent relationship between the
new child table and its parent table(s). Schema modifications to
the parent(s) normally propagate to children as well, and by
default the data of the child table is included in scans of the
parent(s).
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 col-
umn name 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 explic-
itly specifies a default value for the column, this default
overrides any defaults from inherited declarations of the col-
umn. Otherwise, any parents that specify default values for the
column must all specify the same default, or an error will be
reported.
LIKE parent_table [ { INCLUDING | EXCLUDING } DEFAULTS ]
The LIKE clause specifies a table from which the new table auto-
matically copies all column names, their data types, and their
not-null constraints.
Unlike INHERITS, the new table and original table are completely
decoupled after creation is complete. Changes to the original
table will not be applied to the new table, and it is not possi-
ble to include data of the new table in scans of the original
table.
Default expressions for the copied column definitions will only
be copied if INCLUDING DEFAULTS is specified. The default behav-
ior is to exclude default expressions, resulting in all columns
of the new table having null defaults.
WITH OIDS
WITHOUT OIDS
This optional clause specifies whether rows of the new table
should have OIDs (object identifiers) assigned to them. If nei-
ther WITH OIDS nor WITHOUT OIDS is specified, the default value
depends upon the default_with_oids configuration parameter. (If
the new table inherits from any tables that have OIDs, then WITH
OIDS is forced even if the command says WITHOUT OIDS.)
If WITHOUT OIDS is specified or implied, the new table does not
store OIDs and no OID will be assigned for a row inserted into
it. This is generally considered worthwhile, since it will
reduce OID consumption and thereby postpone the wraparound of
the 32-bit OID counter. Once the counter wraps around, OIDs can
no longer be assumed to be unique, which makes them considerably
less useful. In addition, excluding OIDs from a table reduces
the space required to store the table on disk by 4 bytes per row
(on most machines), slightly improving performance.
To remove OIDs from a table after it has been created, use ALTER
TABLE [alter_table(7)].
CONSTRAINT constraint_name
An optional name for a column or table constraint. If not speci-
fied, 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 provided for compatibility with non-standard
SQL databases. Its use is discouraged in new applications.
UNIQUE (column constraint)
UNIQUE ( column_name [, ... ] ) (table constraint)
The UNIQUE constraint specifies that a group of one or more col-
umns of a table may contain only unique values. The behavior of
the unique table constraint is the same as that for column con-
straints, with the additional capability to span multiple col-
umns.
For the purpose of a unique constraint, null values are not con-
sidered 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.)
PRIMARY KEY (column constraint)
PRIMARY KEY ( column_name [, ... ] ) (table constraint)
The primary key constraint specifies that a column or columns of
a table may contain only unique (non-duplicate), nonnull values.
Technically, PRIMARY KEY is merely a combination of UNIQUE and
NOT NULL, but identifying a set of columns as primary key also
provides metadata 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 con-
straint defined for the same table.
CHECK (expression)
The CHECK clause specifies an expression producing a Boolean
result which new or updated rows must satisfy for an insert or
update operation to succeed. Expressions evaluating to TRUE or
UNKNOWN succeed. Should any row of an insert or update operation
produce a FALSE result an error exception is raised and the
insert or update does not alter the database. A check constraint
specified as a column constraint should reference that column's
value only, while an expression appearing in a table constraint
may reference multiple columns.
Currently, CHECK expressions cannot contain subqueries 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 [, ... ] )
These clauses specify a foreign key constraint, which requires
that a group of one or more columns of the new table must only
contain values that match values in the referenced column(s) of
some row of the referenced table. 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 ref-
erenced table. Note that foreign key constraints may not be
defined between temporary tables and permanent tables.
A value inserted into the referencing column(s) is matched
against the values of the referenced table and referenced col-
umns using the given match type. There are three match types:
MATCH FULL, MATCH PARTIAL, and MATCH SIMPLE, which is also the
default. MATCH FULL will not allow one column of a multicolumn
foreign key to be null unless all foreign key columns are null.
MATCH SIMPLE 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 col-
umns. The ON DELETE clause specifies the action to perform when
a referenced row in the referenced table is being deleted. Like-
wise, 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. Referential actions
other than the NO ACTION check cannot be deferred, even if the
constraint is declared deferrable. There are the following pos-
sible actions for each clause:
NO ACTION
Produce an error indicating that the deletion or update
would create a foreign key constraint violation. If the
constraint is deferred, this error will be produced at
constraint check time if there still exist any referenc-
ing rows. This is the default action.
RESTRICT
Produce an error indicating that the deletion or update
would create a foreign key constraint violation. This is
the same as NO ACTION except that the check is not
deferrable.
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(s) to null.
SET DEFAULT
Set the referencing column(s) to their default values.
If the referenced column(s) are changed frequently, it may be wise to
add an index to the foreign key column so that referential actions
associated with the foreign key column can be performed more effi-
ciently.
DEFERRABLE
NOT DEFERRABLE
This controls whether the constraint can be deferred. A con-
straint 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 [set_constraints(7)] command). NOT DEFERRABLE is
the default. Only foreign key constraints currently accept this
clause. All other constraint types are not deferrable.
INITIALLY IMMEDIATE
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 [set_constraints(7)]
command.
ON COMMIT
The behavior of temporary tables at the end of a transaction
block can be controlled using ON COMMIT. The three options are:
PRESERVE ROWS
No special action is taken at the ends of transactions.
This is the default behavior.
DELETE ROWS
All rows in the temporary table will be deleted at the
end of each transaction block. Essentially, an automatic
truncate(7) is done at each commit.
DROP The temporary table will be dropped at the end of the
current transaction block.
TABLESPACE tablespace
The tablespace is the name of the tablespace in which the new
table is to be created. If not specified, default_tablespace is
used, or the database's default tablespace if default_tablespace
is an empty string.
USING INDEX TABLESPACE tablespace
This clause allows selection of the tablespace in which the
index associated with a UNIQUE or PRIMARY KEY constraint will be
created. If not specified, default_tablespace is used, or the
database's default tablespace if default_tablespace is an empty
string.
NOTES
Using OIDs in new applications is not recommended: where possible,
using a SERIAL or other sequence generator as the table's primary key
is preferred. However, if your application does make 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 data-
base-wide unique identifier, use the combination of tableoid and row
OID for the purpose.
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 uniqueness. Thus, it is not nec-
essary to create an index explicitly for primary key columns. (See CRE-
ATE INDEX [create_index(7)] for more information.)
Unique constraints and primary keys are not inherited in the current
implementation. This makes the combination of inheritance and unique
constraints rather dysfunctional.
A table cannot have more than 1600 columns. (In practice, the effective
limit is lower because of tuple-length constraints.)
EXAMPLES
Create table films and table distributors:
CREATE TABLE films (
code char(5) CONSTRAINT firstkey PRIMARY KEY,
title varchar(40) NOT NULL,
did integer NOT NULL,
date_prod date,
kind varchar(10),
len interval hour to minute
);
CREATE TABLE distributors (
did integer PRIMARY KEY DEFAULT nextval('serial'),
name varchar(40) NOT NULL CHECK (name <> '')
);
Create a table with a 2-dimensional array:
CREATE TABLE array_int (
vector int[][]
);
Define a unique table constraint for the table films. Unique table con-
straints can be defined on one or more columns of the table.
CREATE TABLE films (
code char(5),
title varchar(40),
did integer,
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 integer CHECK (did > 100),
name varchar(40)
);
Define a check table constraint:
CREATE TABLE distributors (
did integer,
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 integer,
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 syn-
tax, the second the column constraint syntax.
CREATE TABLE distributors (
did integer,
name varchar(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did integer PRIMARY KEY,
name varchar(40)
);
This assigns a literal constant default value for the column name,
arranges for the default value of column did to be generated by select-
ing the next value of a sequence object, and makes the default value of
modtime 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 integer CONSTRAINT no_null NOT NULL,
name varchar(40) NOT NULL
);
Define a unique constraint for the name column:
CREATE TABLE distributors (
did integer,
name varchar(40) UNIQUE
);
The above is equivalent to the following specified as a table con-
straint:
CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name)
);
Create table cinemas in tablespace diskvol1:
CREATE TABLE cinemas (
id serial,
name text,
location text
) TABLESPACE diskvol1;
COMPATIBILITY
The CREATE TABLE command conforms to the SQL standard, with exceptions
listed below.
TEMPORARY TABLES
Although the syntax of CREATE TEMPORARY TABLE resembles that of the SQL
standard, the effect is not the same. In the standard, temporary tables
are defined just once and automatically exist (starting with empty con-
tents) in every session that needs them. PostgreSQL instead requires
each session to issue its own CREATE TEMPORARY TABLE command for each
temporary table to be used. This allows different sessions to use the
same temporary table name for different purposes, whereas the stan-
dard's approach constrains all instances of a given temporary table
name to have the same table structure.
The standard's definition of the behavior of temporary tables is widely
ignored. PostgreSQL's behavior on this point is similar to that of sev-
eral other SQL databases.
The standard's distinction between global and local temporary tables is
not in PostgreSQL, since that distinction depends on the concept of
modules, which PostgreSQL does not have. For compatibility's sake,
PostgreSQL will accept the GLOBAL and LOCAL keywords in a temporary ta-
ble declaration, but they have no effect.
The ON COMMIT clause for temporary tables also resembles the SQL stan-
dard, but has some differences. If the ON COMMIT clause is omitted,
SQL specifies that the default behavior is ON COMMIT DELETE ROWS. How-
ever, the default behavior in PostgreSQL is ON COMMIT PRESERVE ROWS.
The ON COMMIT DROP option does not exist in SQL.
COLUMN CHECK CONSTRAINTS
The SQL 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.
NULL ``CONSTRAINT''
The NULL ``constraint'' (actually a non-constraint) is a PostgreSQL
extension to the SQL standard that is included for compatibility with
some other database systems (and for symmetry with the NOT NULL con-
straint). Since it is the default for any column, its presence is sim-
ply noise.
INHERITANCE
Multiple inheritance via the INHERITS clause is a PostgreSQL language
extension. SQL:1999 and later define single inheritance using a dif-
ferent syntax and different semantics. SQL:1999-style inheritance is
not yet supported by PostgreSQL.
OBJECT IDS
The PostgreSQL concept of OIDs is not standard.
ZERO-COLUMN TABLES
PostgreSQL allows a table of no columns to be created (for example,
CREATE TABLE foo();). This is an extension from the SQL standard, which
does not allow zero-column tables. Zero-column tables are not in them-
selves very useful, but disallowing them creates odd special cases for
ALTER TABLE DROP COLUMN, so it seems cleaner to ignore this spec
restriction.
TABLESPACES
The PostgreSQL concept of tablespaces is not part of the standard.
Hence, the clauses TABLESPACE and USING INDEX TABLESPACE are exten-
sions.
SEE ALSO
ALTER TABLE [alter_table(7)], DROP TABLE [drop_table(l)], CREATE
TABLESPACE [create_tablespace(l)]
SQL - Language Statements 2010-12-14 CREATE TABLE()
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