create_table.7

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.\\" auto-generated by docbook2man-spec $Revision: 1.1.1.1 $
.TH "CREATE TABLE" "" "2008-01-03" "SQL - Language Statements" "SQL Commands"
.SH NAME
CREATE TABLE \- define a new table

.SH SYNOPSIS
.sp
.nf
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE \fItable_name\fR ( [
  { \fIcolumn_name\fR \fIdata_type\fR [ DEFAULT \fIdefault_expr\fR ] [ \fIcolumn_constraint\fR [ ... ] ]
    | \fItable_constraint\fR
    | LIKE \fIparent_table\fR [ { INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS } ] ... }
    [, ... ]
] )
[ INHERITS ( \fIparent_table\fR [, ... ] ) ]
[ WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE \fItablespace\fR ]

where \fIcolumn_constraint\fR is:

[ CONSTRAINT \fIconstraint_name\fR ]
{ NOT NULL | 
  NULL | 
  UNIQUE \fIindex_parameters\fR |
  PRIMARY KEY \fIindex_parameters\fR |
  CHECK ( \fIexpression\fR ) |
  REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and \fItable_constraint\fR is:

[ CONSTRAINT \fIconstraint_name\fR ]
{ UNIQUE ( \fIcolumn_name\fR [, ... ] ) \fIindex_parameters\fR |
  PRIMARY KEY ( \fIcolumn_name\fR [, ... ] ) \fIindex_parameters\fR |
  CHECK ( \fIexpression\fR ) |
  FOREIGN KEY ( \fIcolumn_name\fR [, ... ] ) REFERENCES \fIreftable\fR [ ( \fIrefcolumn\fR [, ... ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE \fIaction\fR ] [ ON UPDATE \fIaction\fR ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

\fIindex_parameters\fR in UNIQUE and PRIMARY KEY constraints are:

[ WITH ( \fIstorage_parameter\fR [= \fIvalue\fR] [, ... ] ) ]
[ USING INDEX TABLESPACE \fItablespace\fR ]
.sp
.fi
.SH "DESCRIPTION"
.PP
\fBCREATE TABLE\fR will create a new, initially empty table
in the current database. The table will be owned by the user issuing the
command.
.PP
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 name of the table must be
distinct from the name of any other table, sequence, index, or view
in the same schema.
.PP
\fBCREATE TABLE\fR 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.
.PP
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.
.PP
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 for use when the
constraint only affects one column.
.SH "PARAMETERS"
.TP
\fBTEMPORARY or TEMP\fR
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 [\fBcreate_table\fR(7)].
.TP
\fB\fItable_name\fB\fR
The name (optionally schema-qualified) of the table to be created.
.TP
\fB\fIcolumn_name\fB\fR
The name of a column to be created in the new table.
.TP
\fB\fIdata_type\fB\fR
The data type of the column. This may include array
specifiers. For more information on the data types supported by
PostgreSQL, refer to in the documentation.
.TP
\fBDEFAULT\fR
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.
.TP
\fBINHERITS ( \fIparent_table\fB [, ... ] )\fR
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 column 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 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.
.TP
\fBLIKE \fIparent_table\fB [ { INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS } ]\fR
The LIKE clause specifies a table from which
the new table automatically 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
possible 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 behavior is to exclude default expressions, resulting in the
copied columns in the new table having null defaults.

Not-null constraints are always copied to the new table.
CHECK constraints will only be copied if
INCLUDING CONSTRAINTS is specified; other types of
constraints will never be copied. Also, no distinction is made between
column constraints and table constraints \(em when constraints are
requested, all check constraints are copied.

Note also that unlike INHERITS, copied columns and
constraints are not merged with similarly named columns and constraints.
If the same name is specified explicitly or in another
LIKE clause an error is signalled.
.TP
\fBCONSTRAINT \fIconstraint_name\fB\fR
An optional name for a column or table constraint. If the
constraint is violated, the constraint name is present in error messages,
so constraint names like col must be positive can be used
to communicate helpful constraint information to client applications.
(Double-quotes are needed to specify constraint names that contain spaces.)
If a constraint name is not specified, the system generates a name.
.TP
\fBNOT NULL\fR
The column is not allowed to contain null values.
.TP
\fBNULL\fR
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.
.TP
\fBUNIQUE (column constraint)\fR
.TP
\fBUNIQUE ( \fIcolumn_name\fB [, ... ] ) (table constraint)\fR
The UNIQUE constraint specifies that a
group of one or more 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.)
.TP
\fBPRIMARY KEY (column constraint)\fR
.TP
\fBPRIMARY KEY ( \fIcolumn_name\fB [, ... ] ) (table constraint)\fR
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.
.TP
\fBCHECK ( \fIexpression\fB )\fR
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.
.TP
\fBREFERENCES \fIreftable\fB [ ( \fIrefcolumn\fB ) ] [ MATCH \fImatchtype\fB ] [ ON DELETE \fIaction\fB ] [ ON UPDATE \fIaction\fB ] (column constraint)\fR
.TP
\fBFOREIGN KEY ( \fIcolumn\fB [, ... ] )\fR
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 \fIrefcolumn\fR is omitted, the
primary key of the \fIreftable\fR is used. The
referenced columns must be the columns of a unique or primary
key constraint in the referenced 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 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. Referential actions other than the
NO ACTION check cannot be deferred, even if
the constraint is declared deferrable. There are the following possible
actions for each clause:
.RS
.TP
\fBNO ACTION\fR
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 referencing rows. This is the default action.
.TP
\fBRESTRICT\fR
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.
.TP
\fBCASCADE\fR
Delete any rows referencing the deleted row, or update the
value of the referencing column to the new value of the
referenced column, respectively.
.TP
\fBSET NULL\fR
Set the referencing column(s) to null.
.TP
\fBSET DEFAULT\fR
Set the referencing column(s) to their default values.
.RE
.PP

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
efficiently.
.TP
\fBDEFERRABLE\fR
.TP
\fBNOT DEFERRABLE\fR
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 [\fBset_constraints\fR(7)] command).
NOT DEFERRABLE is the default. Only foreign
key constraints currently accept this clause. All other
constraint types are not deferrable.
.TP
\fBINITIALLY IMMEDIATE\fR
.TP
\fBINITIALLY DEFERRED\fR
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 [\fBset_constraints\fR(7)] command.
.TP
\fBWITH ( \fIstorage_parameter\fB [= \fIvalue\fB] [, ... ] )\fR
This clause specifies optional storage parameters for a table or index;
see Storage Parameters [\fBcreate_table\fR(7)] for more
information. The WITH clause for a
table can also include OIDS=TRUE (or just OIDS)
to specify that rows of the new table
should have OIDs (object identifiers) assigned to them, or
OIDS=FALSE to specify that the rows should not have OIDs.
If OIDS is not specified, the default setting depends upon
the default_with_oids configuration parameter.
(If the new table inherits from any tables that have OIDs, then
OIDS=TRUE is forced even if the command says
OIDS=FALSE.)

If OIDS=FALSE 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 [\fBalter_table\fR(7)].