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CREATE
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 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.
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 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 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
TEMPORARY or TEMP
If specified, the table is created as a temporary table. Temporary
tables are automatically dropped at the end of a session, 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 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 Compatibility
[create_table(5)].
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.
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 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
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.
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 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.
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 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.)
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 constraint
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 reference multiple
columns.
Currently, CHECK expressions cannot contain subqueries nor refer to
variables other than columns of the current row.
] [ ON UPDATE action ] (column constraint)
REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE action
FOREIGN KEY ( column [, ... ] )
Theses clauses specify a foreign key constraint, which 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 inserted into 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
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 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.
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 performed.
DEFERRABLE
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
[set_constraints(5)] 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(5)] 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(5) 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 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 [create_index(5)] 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 syntax, 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 constraint:
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 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 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 standard,
but has some differences. If the ON COMMIT clause is omitted, SQL
specifies that the default behavior is ON COMMIT DELETE ROWS. However, 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 constraint).
Since it is the default for any column, its presence is simply 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(5)], DROP TABLE [drop_table(l)]
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