create_table
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 } ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | UNIQUE | PRIMARY KEY |
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 [, ... ] ) |
PRIMARY KEY ( column_name [, ... ] ) |
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
table. The table name must be distinct from the name of any other ta-
ble, 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.
A table cannot have more than 1600 columns. (In practice, the effec-
tive 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 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 defi-
nition. A table constraint definition is not tied to a particular col-
umn, and it can encompass more than one column. Every column
constraint can also be written as a table constraint; a column con-
straint is only a notational convenience if the constraint only
affects one column.
PARAMETERS
TEMPORARY or TEMP
If specified, the table is created as a temporary table. Tem-
porary tables are automatically dropped at the end of a ses-
sion, or optionally at the end of the current transaction (see
ON COMMIT below). Existing permanent tables with the same name
are not visible to the current session while the temporary ta-
ble exists, unless they are referenced with schema-qualified
names. Any indexes created on a temporary table are automati-
cally 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.
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.
LIKE parent_table [ { INCLUDING | EXCLUDING } DEFAULTS ]
The LIKE clause specifies a table from which the new table
automatically inherits all column names, their data types, and
not-null constraints.
Unlike INHERITS, the new table and inherited table are complete
decoupled after creation has been completed. Data inserted into
the new table will not be reflected into the parent table.
Default expressions for the inherited column definitions will
only be included if INCLUDING DEFAULTS is specified. The
default is to exclude default expressions.
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 dupli-
cate columns are merged to form a single column in the new ta-
ble. 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
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 post-
pone 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. Specifying WITHOUT
OIDS also reduces the space required to store the table on disk
by 4 bytes per row of the table, thereby improving performance.
CONSTRAINT constraint_name
An optional name for a column or table constraint. If not spec-
ified, 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-stan-
dard 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
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 mul-
tiple 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.)
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 pri-
mary 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. A check constraint specified as a
column constraint should reference that column’s value only,
while an expression appearing in a table constraint may refer-
ence 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 [, ... ] )
Theses clauses specify a foreign key constraint, which speci-
fies that a group of one or more columns of the new table must
only contain values which match against values in the refer-
enced 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 pri-
mary key constraint in the referenced table.
A value inserted into these columns is matched against the val-
ues of the referenced table and referenced columns 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 ta-
ble’s columns. The ON DELETE clause specifies the action to
perform 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 except that this action will not be
deferred even if the rest of the constraint is
deferrable and deferred.
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 foreign key column so that NO ACTION and CASCADE actions
associated with the foreign key column can be more efficiently per-
formed.
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 cur-
rently 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 INI-
TIALLY 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_con-
straints(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.
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 neces-
sary, 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 [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.
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 (
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 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 notation.
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
selecting 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)
);
COMPATIBILITY
The CREATE TABLE command conforms to SQL92 and to a subset of SQL99,
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 contents) 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
standard’s approach constrains all instances of a given temporary ta-
ble 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 several 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
table 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. SQL99 (but not SQL92) defines single inheritance using a
different syntax and different semantics. SQL99-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
themselves very useful, but disallowing them creates odd special cases
for ALTER TABLE DROP COLUMN, so it seems cleaner to ignore this spec
restriction.
SEE ALSO
ALTER TABLE [alter_table(7)], DROP TABLE [drop_table(l)]
SQL - Language Statements 2008-01-03 CREATE TABLE()
