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CREATE TABLE

Name

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 [, ...] ) ]
  

Inputs

TEMPORARY

The table is created only for this session, and is automatically dropped on session exit. Existing permanent tables with the same name are not visible while the temporary table exists.

table

The name of a new table to be created.

column

The name of a column.

type

The type of the column. This may include array specifiers. Refer to the PostgreSQL User's Guide for further information about data types and arrays.

DEFAULT value

A default value for a column. See the DEFAULT clause for more information.

column_constraint_clause

The optional column constraint clauses specify a list of integrity 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. Although SQL92 requires the column_constraint_clause to refer to that column only, Postgres allows multiple columns to be referenced within a single column constraint. See the column constraint clause for more information.

table_constraint_clause

The optional table CONSTRAINT clause specifies a list of integrity constraints which new or updated entries must satisfy for an insert or update operation to succeed. Each constraint must evaluate to a boolean expression. Multiple columns may be referenced within a single constraint. Only one PRIMARY KEY clause may be specified for a table; PRIMARY KEY column (a table constraint) and PRIMARY KEY (a column constraint) are mutually exclusive.. See the table constraint clause for more information.

INHERITS inherited_table

The optional INHERITS clause specifies a collection of table names from which this table automatically inherits all fields. If any inherited field name appears more than once, Postgres reports an error. Postgres automatically allows the created table to inherit functions on tables above it in the inheritance hierarchy.

Aside: Inheritance of functions is done according to the conventions of the Common Lisp Object System (CLOS).

Outputs

CREATE

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 runtime, if the table specified already exists in the database.

ERROR: DEFAULT: type mismatched

If data type of default value doesn't match the column definition's data type.

Description

CREATE TABLE will enter a new table into the current data base. The table will be "owned" by the user issuing the command.

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 Clause

DEFAULT value
   

Inputs

value

The possible values for the default value expression are:

  • a literal value

  • a user function

  • a niladic function

Outputs

None.

Description

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:

niladic USER
CURRENT_USER / USER

See CURRENT_USER function

SESSION_USER

not yet supported

SYSTEM_USER

not yet supported

niladic datetime
CURRENT_DATE

See CURRENT_DATE function

CURRENT_TIME

See CURRENT_TIME function

CURRENT_TIMESTAMP

See CURRENT_TIMESTAMP function

In the current release (v6.5), Postgres evaluates all default expressions at the time the table is defined. Hence, functions which are "non-cacheable" such as CURRENT_TIMESTAMP may not produce the desired effect. For the particular case of date/time types, one can work around this behavior by using “DEFAULT TEXT 'now'” instead of “DEFAULT 'now'” or “DEFAULT CURRENT_TIMESTAMP”. This forces Postgres to consider the constant a string type and then to convert the value to timestamp at runtime.

Usage

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'
);
    

Column CONSTRAINT Clause

[ CONSTRAINT name ] { [
    NULL | NOT NULL ] | UNIQUE | PRIMARY KEY | CHECK constraint } [, ...]
   

Inputs

name

An arbitrary name given to the integrity constraint. If name is not specified, it is generated from the table and column names, which should ensure uniqueness for name.

NULL

The column is allowed to contain NULL values. This is the default.

NOT NULL

The column is not allowed to contain NULL values. This is equivalent to the column constraint CHECK (column NOT NULL).

UNIQUE

The column must have unique values. In Postgres this is enforced by an implicit creation of a unique index on the table.

PRIMARY KEY

This column is a primary key, which implies that uniqueness is enforced by the system and that other tables may rely on this column as a unique identifier for rows. See PRIMARY KEY for more information.

constraint

The definition of the constraint.

Description

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

Note: Postgres does not yet (at release 6.5) support REFERENCES integrity constraints. The parser accepts the REFERENCES syntax but ignores the clause.

NOT NULL Constraint

[ 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.

Outputs

status
ERROR: ExecAppend: Fail to add null value in not null attribute "column".

This error occurs at runtime if one tries to insert a null value into a column which has a NOT NULL constraint.

Description

Usage

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
);
     

UNIQUE Constraint

[ CONSTRAINT name ] UNIQUE
   

Inputs

CONSTRAINT name

An arbitrary label given to a constraint.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index.

This error occurs at runtime if one tries to insert a duplicate value into a column.

Description

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.

Usage

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)
);
     

The CHECK Constraint

[ CONSTRAINT name ] CHECK
    ( condition [, ...] ) 
   

Inputs

name

An arbitrary name given to a constraint.

condition

Any valid conditional expression evaluating to a boolean result.

Outputs

status

ERROR: ExecAppend: rejected due to CHECK constraint "table_column".

This error occurs at runtime if one tries to insert an illegal value into a column subject to a CHECK constraint.

Description

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.

PRIMARY KEY Constraint

[ CONSTRAINT name ] PRIMARY KEY 
   

Inputs

CONSTRAINT name

An arbitrary name for the constraint.

Outputs

ERROR: Cannot insert a duplicate key into a unique index.

This occurs at run-time if one tries to insert a duplicate value into a column subject to a PRIMARY KEY constraint.

Description

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.

Notes

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.

Table CONSTRAINT Clause

[ CONSTRAINT name ] { PRIMARY KEY |  UNIQUE } ( column [, ...] )
[ CONSTRAINT name ] CHECK ( constraint )
   

Inputs

CONSTRAINT name

An arbitrary name given to an integrity constraint.

column [, ...]

The column name(s) for which to define a unique index and, for PRIMARY KEY, a NOT NULL constraint.

CHECK ( constraint )

A boolean expression to be evaluated as the constraint.

Outputs

The possible outputs for the table constraint clause are the same as for the corresponding portions of the column constraint clause.

Description

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

Note: Postgres does not yet (as of version 6.5) support FOREIGN KEY integrity constraints. The parser understands the FOREIGN KEY syntax, but only prints a notice and otherwise ignores the clause. Foreign keys may be partially emulated by triggers (See the CREATE TRIGGER statement).

UNIQUE Constraint

[ CONSTRAINT name ] UNIQUE ( column [, ...] )
    

Inputs

CONSTRAINT name

An arbitrary name given to a constraint.

column

A name of a column in a table.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index

This error occurs at runtime if one tries to insert a duplicate value into a column.

Description

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.

Usage

Define a UNIQUE table constraint for the table distributors:

CREATE TABLE distributors (
    did      DECIMAL(03),
    name     VARCHAR(40),
    UNIQUE(name)
);
     

PRIMARY KEY Constraint

[ CONSTRAINT name ] PRIMARY KEY ( column [, ...] ) 
    

Inputs

CONSTRAINT name

An arbitrary name for the constraint.

column [, ...]

The names of one or more columns in the table.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index.

This occurs at run-time if one tries to insert a duplicate value into a column subject to a PRIMARY KEY constraint.

Description

The PRIMARY KEY constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique, (non duplicate), 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.

Usage

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(03) 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(03),
    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(05),
    title     VARCHAR(40),
    did       DECIMAL(03),
    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(03),
    name     CHAR VARYING(40),
    PRIMARY KEY(did)
); 
   
CREATE TABLE distributors (
    did      DECIMAL(03) PRIMARY KEY,
    name     VARCHAR(40)
);
   

Notes

CREATE TABLE/INHERITS is a Postgres language extension.

Compatibility

SQL92

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(03),
    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 share 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.

NOT DEFERRABLE

means that the Constraint must be checked for violation of its rule after the execution of every SQL statement.

DEFERRABLE

means that checking of the Constraint may be deferred until some later time, but no later than the end of the current transaction.

The constraint mode for every Constraint always has an initial default value which is set for that Constraint at the beginning of a transaction.

INITIALLY IMMEDIATE

means that, as of the start of the transaction, the Constraint must be checked for violation of its rule after the execution of every SQL statement.

INITIALLY DEFERRED

means that, as of the start of the transaction, checking of the Constraint may be deferred until some later time, but no later than the end of the current transaction.

CHECK clause

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 ]
     
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