Provided by: postgres-xc-client_1.1-2ubuntu2_amd64 
NAME
CREATE_TABLE - define a new table
SYNOPSIS
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [
{ column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
| table_constraint
| LIKE source_table [ like_option ... ] }
[, ... ]
] )
[ INHERITS ( parent_table [, ... ] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
[ DISTRIBUTE BY { REPLICATION | ROUNDROBIN | { [HASH | MODULO ] ( column_name ) } } ]
[ TO { GROUP groupname | NODE ( nodename [, ... ] ) } ]
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name
OF type_name [ (
{ column_name WITH OPTIONS [ column_constraint [ ... ] ]
| table_constraint }
[, ... ]
) ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
[ DISTRIBUTE BY { REPLICATION | ROUNDROBIN | { [HASH | MODULO ] ( column_name ) } } ]
[ TO { GROUP groupname | NODE ( nodename [, ... ] ) } ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL |
NULL |
CHECK ( expression ) [ NO INHERIT ] |
DEFAULT default_expr |
UNIQUE index_parameters |
PRIMARY KEY index_parameters |
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 ]
{ CHECK ( expression ) [ NO INHERIT ] |
UNIQUE ( column_name [, ... ] ) index_parameters |
PRIMARY KEY ( column_name [, ... ] ) index_parameters |
EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE ( predicate ) ] |
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 ]
and like_option is:
{ INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES | STORAGE | COMMENTS | ALL }
index_parameters in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ USING INDEX TABLESPACE tablespace_name ]
exclude_element in an EXCLUDE constraint is:
{ column_name | ( expression ) } [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
DESCRIPTION
Note
The syntax of CREATE TABLE applies only to Postgres-XC.
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 cannot be given when creating a temporary table. The name of the table must be
distinct from the name of any other table, sequence, index, view, or foreign table 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.
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.
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.
To be able to create a table, you must have USAGE privilege on all column types or the type in the OF
clause, respectively.
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.
The autovacuum daemon cannot access and therefore cannot vacuum or analyze temporary tables. For this
reason, appropriate vacuum and analyze operations should be performed via session SQL commands. For
example, if a temporary table is going to be used in complex queries, it is wise to run ANALYZE on
the temporary table after it is populated.
Optionally, GLOBAL or LOCAL can be written before TEMPORARY or TEMP. This presently makes no
difference in Postgres-XC and is deprecated; see COMPATIBILITY.
UNLOGGED
If specified, the table is created as an unlogged table. Data written to unlogged tables is not
written to the write-ahead log (see Chapter 28, Reliability and the Write-Ahead Log, in the
documentation), which makes them considerably faster than ordinary tables. However, they are not
crash-safe: an unlogged table is automatically truncated after a crash or unclean shutdown. The
contents of an unlogged table are also not replicated to standby servers. Any indexes created on an
unlogged table are automatically unlogged as well; however, unlogged GiST indexes are currently not
supported and cannot be created on an unlogged table.
IF NOT EXISTS
Do not throw an error if a relation with the same name already exists. A notice is issued in this
case. Note that there is no guarantee that the existing relation is anything like the one that would
have been created.
table_name
The name (optionally schema-qualified) of the table to be created.
OF type_name
Creates a typed table, which takes its structure from the specified composite type (name optionally
schema-qualified). A typed table is tied to its type; for example the table will be dropped if the
type is dropped (with DROP TYPE ... CASCADE).
When a typed table is created, then the data types of the columns are determined by the underlying
composite type and are not specified by the CREATE TABLE command. But the CREATE TABLE command can
add defaults and constraints to the table and can specify storage parameters.
column_name
The name of a column to be created in the new table.
data_type
The data type of the column. This can include array specifiers. For more information on the data
types supported by Postgres-XC, refer to Chapter 8, Data Types, in the documentation.
COLLATE collation
The COLLATE clause assigns a collation to the column (which must be of a collatable data type). If
not specified, the column data type's default collation is used.
INHERITS ( parent_table [, ... ] )
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. 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.
Note
The following description applies only to Postgres-XC
It is currently not possible to distribute a table with more than one parent.
Note
The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
CHECK constraints are merged in essentially the same way as columns: if multiple parent tables and/or
the new table definition contain identically-named CHECK constraints, these constraints must all have
the same check expression, or an error will be reported. Constraints having the same name and
expression will be merged into one copy. A constraint marked NO INHERIT in a parent will not be
considered. Notice that an unnamed CHECK constraint in the new table will never be merged, since a
unique name will always be chosen for it.
Column STORAGE settings are also copied from parent tables.
LIKE source_table [ like_option ... ]
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 constraintswhen constraints are requested,
all check constraints are copied.
Any indexes on the original table will not be created on the new table, unless the INCLUDING INDEXES
clause is specified.
STORAGE settings for the copied column definitions will only be copied if INCLUDING STORAGE is
specified. The default behavior is to exclude STORAGE settings, resulting in the copied columns in
the new table having type-specific default settings. For more on STORAGE settings, see Section 58.2,
“TOAST”, in the documentation.
Comments for the copied columns, constraints, and indexes will only be copied if INCLUDING COMMENTS
is specified. The default behavior is to exclude comments, resulting in the copied columns and
constraints in the new table having no comments.
INCLUDING ALL is an abbreviated form of INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES
INCLUDING STORAGE INCLUDING COMMENTS.
Note also that unlike INHERITS, columns and constraints copied by LIKE 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.
The LIKE clause can also be used to copy columns from views, foreign tables, or composite types.
Inapplicable options (e.g., INCLUDING INDEXES from a view) are ignored.
CONSTRAINT constraint_name
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.
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 provided for compatibility with non-standard SQL databases. Its use is
discouraged in new applications.
CHECK ( expression ) [ NO INHERIT ]
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 can reference multiple columns.
Currently, CHECK expressions cannot contain subqueries nor refer to variables other than columns of
the current row.
A constraint marked with NO INHERIT will not propagate to child tables.
DEFAULT default_expr
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.
UNIQUE (column constraint), UNIQUE ( column_name [, ... ] ) (table constraint)
The UNIQUE constraint specifies that a group of one or more columns of a table can 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.
Note
The following description applies only to Postgres-XC
In Postgres-XC, if DISTRIBUTE BY REPLICATION is not specified, only the distribution key is allowed
to have this constraint.
Note
The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
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 can 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 can 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.
If DISTRIBUTE BY REPLICATION is not specified, the distribution key must be included in the set of
primary key columns.
EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE (
predicate ) ]
The EXCLUDE clause defines an exclusion constraint, which guarantees that if any two rows are
compared on the specified column(s) or expression(s) using the specified operator(s), not all of
these comparisons will return TRUE. If all of the specified operators test for equality, this is
equivalent to a UNIQUE constraint, although an ordinary unique constraint will be faster. However,
exclusion constraints can specify constraints that are more general than simple equality. For
example, you can specify a constraint that no two rows in the table contain overlapping circles (see
Section 8.8, “Geometric Types”, in the documentation) by using the && operator.
Exclusion constraints are implemented using an index, so each specified operator must be associated
with an appropriate operator class (see Section 11.9, “Operator Classes and Operator Families”, in
the documentation) for the index access method index_method. The operators are required to be
commutative. Each exclude_element can optionally specify an operator class and/or ordering options;
these are described fully under CREATE INDEX (CREATE_INDEX(7)).
The access method must support amgettuple (see Chapter 54, Index Access Method Interface Definition,
in the documentation); at present this means GIN cannot be used. Although it's allowed, there is
little point in using B-tree or hash indexes with an exclusion constraint, because this does nothing
that an ordinary unique constraint doesn't do better. So in practice the access method will always be
GiST or SP-GiST.
The predicate allows you to specify an exclusion constraint on a subset of the table; internally this
creates a partial index. Note that parentheses are required around the predicate.
REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ]
(column constraint), FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] (table constraint)
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 refcolumn is omitted, the primary key of the reftable is used. The
referenced columns must be the columns of a non-deferrable unique or primary key constraint in the
referenced table. Note that foreign key constraints cannot 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:
NO ACTION
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.
RESTRICT
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.
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(s) to null.
SET DEFAULT
Set the referencing column(s) to their default values.
If the referenced column(s) are changed frequently, it might 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.
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 can be postponed
until the end of the transaction (using the SET CONSTRAINTS (SET_CONSTRAINTS(7)) command). NOT
DEFERRABLE is the default. Currently, only UNIQUE, PRIMARY KEY, EXCLUDE, and REFERENCES (foreign key)
constraints accept this clause. NOT NULL and CHECK constraints 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(7)) command.
WITH ( storage_parameter [= value] [, ... ] )
This clause specifies optional storage parameters for a table or index; see Storage Parameters 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 (ALTER_TABLE(7)).
WITH OIDS, WITHOUT OIDS
These are obsolescent syntaxes equivalent to WITH (OIDS) and WITH (OIDS=FALSE), respectively. If you
wish to give both an OIDS setting and storage parameters, you must use the WITH ( ... ) syntax; see
above.
Note
The following description applies only to Postgres-XC
In Postgres-XC, OID is kept locally in each Datanode and Coordinator. The OID value may inconsistent
for rows stored in different Datanodes.
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.
TABLESPACE tablespace_name
The tablespace_name is the name of the tablespace in which the new table is to be created. If not
specified, default_tablespace is consulted, or temp_tablespaces if the table is temporary.
USING INDEX TABLESPACE tablespace_name
This clause allows selection of the tablespace in which the index associated with a UNIQUE, PRIMARY
KEY, or EXCLUDE constraint will be created. If not specified, default_tablespace is consulted, or
temp_tablespaces if the table is temporary.
DISTRIBUTE BY
Note
The following description applies only to Postgres-XC
This clause specifies how the table is distributed or replicated among Datanodes.
REPLICATION
Each row of the table will be replicated into all the Datanode of the Postgres-XC database
cluster.
ROUNDROBIN
Each row of the table will be placed in one of the Datanodes by round-robin manner. The value of
the row will not be needed to determine what Datanode to go.
HASH ( column_name )
Each row of the table will be placed based on the hash value of the specified column. Following
type is allowed as distribution column: INT8, INT2, OID, INT4, BOOL, INT2VECTOR, OIDVECTOR, CHAR,
NAME, TEXT, BPCHAR, BYTEA, VARCHAR, FLOAT4, FLOAT8, NUMERIC, CASH, ABSTIME, RELTIME, DATE, TIME,
TIMESTAMP, TIMESTAMPTZ, INTERVAL, and TIMETZ.
Please note that floating point is not allowed as a basis of the distribution column.
MODULO ( column_name )
Each row of the table will be placed based on the modulo of the specified column. Following type
is allowed as distribution column: INT8, INT2, OID, INT4, BOOL, INT2VECTOR, OIDVECTOR, CHAR,
NAME, TEXT, BPCHAR, BYTEA, VARCHAR, FLOAT4, FLOAT8, NUMERIC, CASH, ABSTIME, RELTIME, DATE, TIME,
TIMESTAMP, TIMESTAMPTZ, INTERVAL, and TIMETZ.
Please note that floating point is not allowed as a basis of the distribution column.
If DISTRIBUTE BY is not specified, columns with UNIQUE constraint will be chosen as the distribution
key. If no such column is specified, distribution column is the first eligible column in the
definition. If no such column is found, then the table will be distributed by ROUNDROBIN.
TO GROUP, TO NODE
This defines on the list of nodes on which table data exists. If this is not specified table data is
present on all Datanodes.
nodename
Associated with TO NODE, it defines a Postgres-XC node of catalog pgxc_node.
groupname
Associated with TO GROUP, it defines a Postgres-XC node group in catalog pgxc_group.
Storage Parameters
The WITH clause can specify storage parameters for tables, and for indexes associated with a UNIQUE,
PRIMARY KEY, or EXCLUDE constraint. Storage parameters for indexes are documented in CREATE INDEX
(CREATE_INDEX(7)). The storage parameters currently available for tables are listed below. For each
parameter, unless noted, there is an additional parameter with the same name prefixed with toast., which
can be used to control the behavior of the table's secondary TOAST table, if any (see Section 58.2,
“TOAST”, in the documentation for more information about TOAST). Note that the TOAST table inherits the
autovacuum_* values from its parent table, if there are no toast.autovacuum_* settings set.
fillfactor (integer)
The fillfactor for a table is a percentage between 10 and 100. 100 (complete packing) is the default.
When a smaller fillfactor is specified, INSERT operations pack table pages only to the indicated
percentage; the remaining space on each page is reserved for updating rows on that page. This gives
UPDATE a chance to place the updated copy of a row on the same page as the original, which is more
efficient than placing it on a different page. For a table whose entries are never updated, complete
packing is the best choice, but in heavily updated tables smaller fillfactors are appropriate. This
parameter cannot be set for TOAST tables.
autovacuum_enabled, toast.autovacuum_enabled (boolean)
Enables or disables the autovacuum daemon on a particular table. If true, the autovacuum daemon will
initiate a VACUUM operation on a particular table when the number of updated or deleted tuples
exceeds autovacuum_vacuum_threshold plus autovacuum_vacuum_scale_factor times the number of live
tuples currently estimated to be in the relation. Similarly, it will initiate an ANALYZE operation
when the number of inserted, updated or deleted tuples exceeds autovacuum_analyze_threshold plus
autovacuum_analyze_scale_factor times the number of live tuples currently estimated to be in the
relation. If false, this table will not be autovacuumed, except to prevent transaction Id wraparound.
See Section 22.1.5, “Preventing Transaction ID Wraparound Failures”, in the documentation for more
about wraparound prevention. Observe that this variable inherits its value from the autovacuum
setting.
autovacuum_vacuum_threshold, toast.autovacuum_vacuum_threshold (integer)
Minimum number of updated or deleted tuples before initiate a VACUUM operation on a particular table.
autovacuum_vacuum_scale_factor, toast.autovacuum_vacuum_scale_factor (float4)
Multiplier for reltuples to add to autovacuum_vacuum_threshold.
autovacuum_analyze_threshold (integer)
Minimum number of inserted, updated, or deleted tuples before initiate an ANALYZE operation on a
particular table.
autovacuum_analyze_scale_factor (float4)
Multiplier for reltuples to add to autovacuum_analyze_threshold.
autovacuum_vacuum_cost_delay, toast.autovacuum_vacuum_cost_delay (integer)
Custom autovacuum_vacuum_cost_delay parameter.
autovacuum_vacuum_cost_limit, toast.autovacuum_vacuum_cost_limit (integer)
Custom autovacuum_vacuum_cost_limit parameter.
autovacuum_freeze_min_age, toast.autovacuum_freeze_min_age (integer)
Custom vacuum_freeze_min_age parameter. Note that autovacuum will ignore attempts to set a per-table
autovacuum_freeze_min_age larger than the half system-wide autovacuum_freeze_max_age setting.
autovacuum_freeze_max_age, toast.autovacuum_freeze_max_age (integer)
Custom autovacuum_freeze_max_age parameter. Note that autovacuum will ignore attempts to set a
per-table autovacuum_freeze_max_age larger than the system-wide setting (it can only be set smaller).
Note that while you can set autovacuum_freeze_max_age very small, or even zero, this is usually
unwise since it will force frequent vacuuming.
autovacuum_freeze_table_age, toast.autovacuum_freeze_table_age (integer)
Custom vacuum_freeze_table_age parameter.
NOTES
Using OIDs in new applications is not recommended: where possible.
Tip
The use of OIDS=FALSE 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.
Postgres-XC automatically creates an index for each unique constraint and primary key constraint to
enforce uniqueness. Thus, it is not necessary to create an index explicitly 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.
A table cannot have more than 1600 columns. (In practice, the effective limit is usually lower because of
tuple-length constraints.)
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_int (
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:
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 syntax:
CREATE TABLE distributors (
did integer,
name varchar(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did integer PRIMARY KEY,
name varchar(40)
);
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 same, specified as a table constraint:
CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name)
);
Create the same table, specifying 70% fill factor for both the table and its unique index:
CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name) WITH (fillfactor=70)
)
WITH (fillfactor=70);
Create table circles with an exclusion constraint that prevents any two circles from overlapping:
CREATE TABLE circles (
c circle,
EXCLUDE USING gist (c WITH &&)
);
Create table cinemas in tablespace diskvol1:
CREATE TABLE cinemas (
id integer,
name text,
location text
) TABLESPACE diskvol1;
Create a composite type and a typed table:
CREATE TYPE employee_type AS (name text, salary numeric);
CREATE TABLE employees OF employee_type (
PRIMARY KEY (name),
salary WITH OPTIONS DEFAULT 1000
);
COMPATIBILITY
The CREATE TABLE command conforms to the SQL standard, 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. Postgres-XC 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. Postgres-XC's behavior
on this point is similar to that of several other SQL databases.
The SQL standard also distinguishes between global and local temporary tables, where a local temporary
table has a separate set of contents for each SQL module within each session, though its definition is
still shared across sessions. Since Postgres-XC does not support SQL modules, this distinction is not
relevant in Postgres-XC.
For compatibility's sake, Postgres-XC will accept the GLOBAL and LOCAL keywords in a temporary table
declaration, but they currently have no effect. Use of these keywords is discouraged, since future
versions of Postgres-XC might adopt a more standard-compliant interpretation of their meaning.
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 Postgre-XC is ON COMMIT PRESERVE ROWS. The ON COMMIT DROP option does
not exist in SQL.
Non-deferred Uniqueness Constraints
When a UNIQUE or PRIMARY KEY constraint is not deferrable, Postgres-XC checks for uniqueness immediately
whenever a row is inserted or modified. The SQL standard says that uniqueness should be enforced only at
the end of the statement; this makes a difference when, for example, a single command updates multiple
key values. To obtain standard-compliant behavior, declare the constraint as DEFERRABLE but not deferred
(i.e., INITIALLY IMMEDIATE). Be aware that this can be significantly slower than immediate uniqueness
checking.
Column Check Constraints
The SQL standard says that CHECK column constraints can only refer to the column they apply to; only
CHECK table constraints can refer to multiple columns. Postgres-XC does not enforce this restriction; it
treats column and table check constraints alike.
EXCLUDE Constraint
The EXCLUDE constraint type is a Postgres-XC extension.
NULL “Constraint”
The NULL“constraint” (actually a non-constraint) is a Postgres-XC 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 Postgres-XC language extension. SQL:1999 and later
define single inheritance using a different syntax and different semantics. SQL:1999-style inheritance is
not yet supported by Postgres-XC.
Zero-column Tables
Postgres-XC 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.
WITH Clause
The WITH clause is a Postgres-XC extension; neither storage parameters nor OIDs are in the standard.
Tablespaces
The Postgres-XC concept of tablespaces is not part of the standard. Hence, the clauses TABLESPACE and
USING INDEX TABLESPACE are extensions.
Typed Tables
Typed tables implement a subset of the SQL standard. According to the standard, a typed table has columns
corresponding to the underlying composite type as well as one other column that is the “self-referencing
column”. Postgres-XC does not support these self-referencing columns explicitly, but the same effect can
be had using the OID feature.
Postgres-XC Specifics
Note
The following description applies only to Postgres-XC
So far, non-immutable functions are not allowed as DEFAULT values.
PRIMARY KEY and foreign key must include the distribution column.
TEMP tables and exclusion constraint are not supported yet.
In Postgres-XC, OID is kept locally in each Datanode and Coordinator. The OID value may inconsistent for
rows stored in different Datanodes.
SEE ALSO
ALTER TABLE (ALTER_TABLE(7)), DROP TABLE (DROP_TABLE(7)), CREATE TABLESPACE (CREATE_TABLESPACE(7)),
CREATE TYPE (CREATE_TYPE(7))