CREATE TABLE -- Creates a new table
CREATE [ TEMPORARY TEMP ] TABLE table (
column type [ NULL NOT NULL ] [ UNIQUE ] [ DEFAULT value ] [column_constraint_clause PRIMARY KEY } [ ... ] ] [, ... ]
[, PRIMARY KEY ( column [, ...] ) ] [, CHECK ( condition ) ] [, table_constraint_clause ]
) [ INHERITS ( inherited_table [, ...] ) ]
CREATE TABLE will enter a new class or table into the current data base. The table will be "owned" by the user issuing the command.
Each type may be a simple type, a complex type (set) or an array type. Each attribute may be specified to be non-null and each may have a default value, specified by the DEFAULT Clause.
Note: Consistent array dimensions within an attribute are not enforced. This will likely change in a future release.
The optional INHERITS clause specifies a collection of class names from which this class automatically inherits all fields. If any inherited field name appears more than once, Postgres reports an error. Postgres automatically allows the created class to inherit functions on classes above it in the inheritance hierarchy. Inheritance of functions is done according to the conventions of the Common Lisp Object System (CLOS).
Each new table or class table is automatically created as a type. Therefore, one or more instances from the class are automatically a type and can be used in ALTER TABLE or other CREATE TABLE statements.
The new table is created as a heap with no initial data. A table can have no more than 1600 columns (realistically, this is limited by the fact that tuple sizes must be less than 8192 bytes), but this limit may be configured lower at some sites. A table cannot have the same name as a system catalog table.
DEFAULT value
None.
The DEFAULT clause assigns a default data value to a column (via a column definition in the CREATE TABLE statement). The data type of a default value must match the column definition's data type.
An INSERT operation that includes a column without a specified default value will assign the NULL value to the column if no explicit data value is provided for it. Default literal means that the default is the specified constant value. Default niladic-function or user-function means that the default is the value of the specified function at the time of the INSERT.
There are two types of niladic functions:
To assign a constant value as the default for the columns did and number, and a string literal to the column did:
CREATE TABLE video_sales (
did VARCHAR(40) DEFAULT 'luso films',
number INTEGER DEFAULT 0,
total CASH DEFAULT '$0.0'
);
To assign an existing sequence as the default for the column did, and
a literal to the column name:
CREATE TABLE distributors (
did DECIMAL(3) DEFAULT NEXTVAL('serial'),
name VARCHAR(40) DEFAULT 'luso films'
);
[ CONSTRAINT name ] {
[ NULL NOT NULL ] UNIQUE PRIMARY KEY CHECK constraint
REFERENCES reftable (refcolumn ) [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] [ [ NOT ] DEFERRABLE ] [ INITIALLY checktime ] } [, ...]
The optional constraint clauses specify constraints or tests which new or updated entries must satisfy for an insert or update operation to succeed. Each constraint must evaluate to a boolean expression. Multiple attributes may be referenced within a single constraint. The use of PRIMARY KEY as a table constraint is mutually incompatible with PRIMARY KEY as a column constraint.
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 Base Table.
There are two ways to define integrity constraints: table constraints, covered later, and column constraints, covered here.
A column constraint is an integrity constraint defined as part of a column definition, and logically becomes a table constraint as soon as it is created. The column constraints available are:
PRIMARY KEY
REFERENCES
UNIQUE
CHECK
NOT NULL
[ CONSTRAINT name ] NOT NULL
The NOT NULL constraint specifies a rule that a column may contain only non-null values. This is a column constraint only, and not allowed as a table constraint.
Define two NOT NULL column constraints on the table distributors, one of which being a named constraint:
CREATE TABLE distributors (
did DECIMAL(3) CONSTRAINT no_null NOT NULL,
name VARCHAR(40) NOT NULL
);
[ CONSTRAINT name ] UNIQUE
The UNIQUE constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique values.
The column definitions of the specified columns do not have to include a NOT NULL constraint to be included in a UNIQUE constraint. Having more than one null value in a column without a NOT NULL constraint, does not violate a UNIQUE constraint. (This deviates from the SQL92 definition, but is a more sensible convention. See the section on compatibility for more details.)
Each UNIQUE column constraint must name a column that is different from the set of columns named by any other UNIQUE or PRIMARY KEY constraint defined for the table.
Note: Postgres automatically creates a unique index for each UNIQUE constraint, to assure data integrity. See CREATE INDEX for more information.
Defines a UNIQUE column constraint for the table distributors. UNIQUE column constraints can only be defined on one column of the table:
CREATE TABLE distributors ( did DECIMAL(3),
name VARCHAR(40) UNIQUE
);
which is equivalent to the following specified as a table constraint:
CREATE TABLE distributors ( did DECIMAL(3),
name VARCHAR(40),
UNIQUE(name)
);
[ CONSTRAINT name ] CHECK ( condition [, ...] )
The CHECK constraint specifies a restriction on allowed values within a column. The CHECK constraint is also allowed as a table constraint.
The SQL92 CHECK column constraints can only be defined on, and refer to, one column of the table. Postgres does not have this restriction.
[ CONSTRAINT name ] PRIMARY KEY
The PRIMARY KEY column constraint specifies that a column of a table may contain only unique (non-duplicate), non-NULL values. The definition of the specified column does not have to include an explicit NOT NULL constraint to be included in a PRIMARY KEY constraint.
Only one PRIMARY KEY can be specified for a table.
Postgres automatically creates a unique index to assure data integrity (see CREATE INDEX statement).
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, since it will result in duplication of equivalent indexes and unproductive additional runtime overhead. However, Postgres does not specifically disallow this.
[ CONSTRAINT name ] REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] [ [ NOT ] DEFERRABLE ] [ INITIALLY checktime ]
The REFERENCES constraint specifies a rule that a column value is checked against the values of another column. REFERENCES can also be specified as part of a FOREIGN KEY table constraint.
The REFERENCES column constraint specifies that a column of a table must only contain values which match against values in a referenced column of a referenced table.
A value added to this column is matched against the values of the referenced table and referenced column using the given match type. In addition, when the referenced column data is changed, actions are run upon this column's matching data.
Currently Postgres only supports MATCH FULL and a default match type. In addition, the referenced columns are supposed to be the columns of a UNIQUE constraint in the referenced table, however Postgres does not enforce this.
[ CONSTRAINT name ] { PRIMARY KEY UNIQUE } ( column [, ...] ) [ CONSTRAINT name ] CHECK ( constraint ) [ CONSTRAINT name ] FOREIGN KEY ( column [, ...] ) REFERENCES reftable
(refcolumn [, ...] ) [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] [ [ NOT ] DEFERRABLE ] [ INITIALLY checktime ]
The possible outputs for the table constraint clause are the same as for the corresponding portions of the column constraint clause.
A table constraint is an integrity constraint defined on one or more columns of a base table. The four variations of "Table Constraint" are:
UNIQUE
CHECK
PRIMARY KEY
FOREIGN KEY
[ CONSTRAINT name ] UNIQUE ( column [, ...] )
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.
See the section on the UNIQUE column constraint for more details.
Define a UNIQUE table constraint for the table distributors:
CREATE TABLE distributors (
did DECIMAL(3),
name VARCHAR(40),
UNIQUE(name)
);
[ CONSTRAINT name ] PRIMARY KEY ( column [, ...] )
The PRIMARY KEY constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique (nonduplicate), non-null values. The column definitions of the specified columns do not have to include a NOT NULL constraint to be included in a PRIMARY KEY constraint.
The PRIMARY KEY table constraint is similar to that for column constraints, with the additional capability of encompassing multiple columns.
Refer to the section on the PRIMARY KEY column constraint for more information.
[ CONSTRAINT name ] FOREIGN KEY ( column [, ...] ) REFERENCES reftable [ ( refcolumn [, ...] ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] [ [ NOT ] DEFERRABLE ] [ INITIALLY checktime ]
The REFERENCES constraint specifies a rule that a column value is checked against the values of another column. REFERENCES can also be specified as part of a FOREIGN KEY table constraint.
The FOREIGN KEY constraint specifies a rule that a group of one or more distinct columns of a table is related to a group of distinct columns in the referenced table.
The FOREIGN KEY table constraint is similar to that for column constraints, with the additional capability of encompassing multiple columns.
Refer to the section on the FOREIGN KEY column constraint for more information.
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 CHAR(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 CHAR(10),
len INTERVAL HOUR TO MINUTE,
CONSTRAINT code_title PRIMARY KEY(code,title)
);
Defines a PRIMARY KEY column constraint for table distributors. PRIMARY KEY
column constraints can only be defined on one column of the table (the following
two examples are equivalent):
CREATE TABLE distributors (
did DECIMAL(3),
name CHAR VARYING(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did DECIMAL(3) PRIMARY KEY,
name VARCHAR(40)
);
CREATE TABLE/INHERITS is a Postgres language extension.
In addition to the locally visible temporary table, SQL92 also defines a CREATE GLOBAL TEMPORARY TABLE statement, and optionally an ON COMMIT clause:
CREATE GLOBAL TEMPORARY TABLE table ( column type [ DEFAULT value ] [ CONSTRAINT column_constraint ] [, ...] ) [ CONSTRAINT table_constraint ] [ ON COMMIT { DELETE PRESERVE } ROWS ]
For temporary tables, the CREATE GLOBAL TEMPORARY TABLE statement names a new table visible to other clients and defines the table's columns and constraints.
The optional ON COMMIT clause of CREATE TEMPORARY TABLE specifies whether or not the temporary table should be emptied of rows whenever COMMIT is executed. If the ON COMMIT clause is omitted, the default option, ON COMMIT DELETE ROWS, is assumed.
To create a temporary table:
CREATE TEMPORARY TABLE actors (
id DECIMAL(3),
name VARCHAR(40),
CONSTRAINT actor_id CHECK (id < 150)
) ON COMMIT DELETE ROWS;
UNIQUE clause
SQL92 specifies some additional capabilities for UNIQUE:
Table Constraint definition:
[ CONSTRAINT name ] UNIQUE ( column [, ...] ) [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE } ] [ [ NOT ] DEFERRABLE ]
Column Constraint definition:
[ CONSTRAINT name ] UNIQUE [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
NULL clause
The NULL "constraint" (actually a non-constraint) is a Postgres extension to SQL92 is included for symmetry with the NOT NULL clause. Since it is the default for any column, its presence is simply noise. [ CONSTRAINT name ] NULL
NOT NULL clause
SQL92 specifies some additional capabilities for NOT NULL:
[ CONSTRAINT name ] NOT NULL [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
CONSTRAINT clause
SQL92 specifies some additional capabilities for constraints, and also defines assertions and domain constraints. Note: Postgres does not yet support either domains or 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 base table as constraints are, so SQL-92 provides the CREATE ASSERTION statement as an alternate method for defining a constraint:
CREATE ASSERTION name CHECK ( condition )
Domain constraints are defined by CREATE DOMAIN or ALTER DOMAIN statements:
Domain constraint:
[ CONSTRAINT name ] CHECK constraint
[ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
Table constraint definition:
[ CONSTRAINT name ] { PRIMARY KEY ( column , ... ) | FOREIGN KEY constraint | UNIQUE constraint | CHECK constraint } [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
Column constraint definition:
[ CONSTRAINT name ] { NOT NULL | PRIMARY KEY | FOREIGN KEY constraint | UNIQUE | CHECK constraint } [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
A CONSTRAINT definition may contain one deferment attribute clause and/or one
initial constraint mode clause, in any order.
SQL92 specifies some additional capabilities for CHECK in either table or column constraints.
table constraint definition:
[ CONSTRAINT name ] CHECK ( VALUE condition ) [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
column constraint definition:
[ CONSTRAINT name ] CHECK ( VALUE condition ) [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
PRIMARY KEY clause
SQL92 specifies some additional capabilities for PRIMARY KEY:
Table Constraint definition:
[ CONSTRAINT name ] PRIMARY KEY ( column [, ...] ) [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]
Column Constraint definition:
[ CONSTRAINT name ] PRIMARY KEY [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE} ] [ [ NOT ] DEFERRABLE ]