CREATE 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 ]
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 ]
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
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 PostgreSQL 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 30 ), 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.
- 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 PostgreSQL , refer to Chapter 8 .
- 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. Parent tables can be plain tables or foreign tables.
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.
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 be copied only 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. Note that copying defaults that call database-modification functions, such as
nextval, may create a functional linkage between the original and new tables.Not-null constraints are always copied to the new table. CHECK constraints will be copied only if INCLUDING CONSTRAINTS is specified. No distinction is made between column constraints and table constraints.
Indexes, PRIMARY KEY , UNIQUE , and EXCLUDE constraints on the original table will be created on the new table only if INCLUDING INDEXES is specified. Names for the new indexes and constraints are chosen according to the default rules, regardless of how the originals were named. (This behavior avoids possible duplicate-name failures for the new indexes.)
STORAGE settings for the copied column definitions will be copied only 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 65.2 .
Comments for the copied columns, constraints, and indexes will be copied only 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 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 signaled.
The LIKE clause can also be used to copy column definitions 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 (see Section 5.3.1 ). The system column tableoid may be referenced, but not any other system column.
A constraint marked with NO INHERIT will not propagate to child tables.
When a table has multiple CHECK constraints, they will be tested for each row in alphabetical order by name, after checking NOT NULL constraints. ( PostgreSQL versions before 9.5 did not honor any particular firing order for CHECK constraints.)
- 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 a unique table constraint is the same as that of a unique column constraint, with the additional capability to span multiple columns. The constraint therefore enforces that any two rows must differ in at least one of these columns.
For the purpose of a unique constraint, null values are not considered equal.
Each unique constraint should 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, redundant unique constraints will be discarded.)
-
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. 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 the set of columns named by any unique constraint defined for the same table. (Otherwise, the unique constraint is redundant and will be discarded.)
PRIMARY KEY enforces the same data constraints as a combination of UNIQUE and NOT NULL . However, identifying a set of columns as the primary key also provides metadata about the design of the schema, since a primary key implies that other tables can rely on this set of columns as a unique identifier for rows.
Adding a PRIMARY KEY constraint will automatically create a unique btree index on the column or group of columns used in the constraint.
- 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 ) 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 ) 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 .
The access method must support amgettuple (see Chapter 59 ); 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 the refcolumn list 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 the default). MATCH FULL will not allow one column of a multicolumn foreign key to be null unless all foreign key columns are null; if they are all null, the row is not required to have a match in the referenced table. MATCH SIMPLE allows any of the foreign key columns to be null; if any of them are null, the row is not required to have a match in the referenced table. MATCH PARTIAL is not yet implemented. (Of course, NOT NULL constraints can be applied to the referencing column(s) to prevent these cases from arising.)
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 values of the referencing column(s) to the new values of the referenced columns, respectively.
- SET NULL
-
Set the referencing column(s) to null.
- SET DEFAULT
-
Set the referencing column(s) to their default values. (There must be a row in the referenced table matching the default values, if they are not null, or the operation will fail.)
If the referenced column(s) are changed frequently, it might be wise to add an index to the referencing column(s) so that referential actions associated with the foreign key constraint 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 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. Note that deferrable constraints cannot be used as conflict arbitrators in an INSERT statement that includes an ON CONFLICT DO UPDATE clause.
-
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 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 .
-
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.
- 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 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.
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 . The storage parameters currently available for tables are listed below. For many of these parameters, as shown, there is an additional parameter with the same name prefixed with toast. , which controls the behavior of the table's secondary TOAST table, if any (see Section 65.2 for more information about TOAST). If a table parameter value is set and the equivalent toast. parameter is not, the TOAST table will use the table's parameter value.
- 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.
- parallel_workers ( integer )
-
This sets the number of workers that should be used to assist a parallel scan of this table. If not set, the system will determine a value based on the relation size. The actual number of workers chosen by the planner may be less, for example due to the setting of max_worker_processes .
- autovacuum_enabled , toast.autovacuum_enabled ( boolean )
-
Enables or disables the autovacuum daemon for a particular table. If true, the autovacuum daemon will perform automatic VACUUM and/or ANALYZE operations on this table following the rules discussed in Section 24.1.6 . If false, this table will not be autovacuumed, except to prevent transaction ID wraparound. See Section 24.1.5 for more about wraparound prevention. Note that the autovacuum daemon does not run at all (except to prevent transaction ID wraparound) if the autovacuum parameter is false; setting individual tables' storage parameters does not override that. Therefore there is seldom much point in explicitly setting this storage parameter to true , only to false .
- autovacuum_vacuum_threshold , toast.autovacuum_vacuum_threshold ( integer )
-
Per-table value for autovacuum_vacuum_threshold parameter.
- autovacuum_vacuum_scale_factor , toast.autovacuum_vacuum_scale_factor ( floating point )
-
Per-table value for autovacuum_vacuum_scale_factor parameter.
- autovacuum_analyze_threshold ( integer )
-
Per-table value for autovacuum_analyze_threshold parameter.
- autovacuum_analyze_scale_factor ( floating point )
-
Per-table value for autovacuum_analyze_scale_factor parameter.
- autovacuum_vacuum_cost_delay , toast.autovacuum_vacuum_cost_delay ( integer )
-
Per-table value for autovacuum_vacuum_cost_delay parameter.
- autovacuum_vacuum_cost_limit , toast.autovacuum_vacuum_cost_limit ( integer )
-
Per-table value for autovacuum_vacuum_cost_limit parameter.
- autovacuum_freeze_min_age , toast.autovacuum_freeze_min_age ( integer )
-
Per-table value for vacuum_freeze_min_age parameter. Note that autovacuum will ignore per-table autovacuum_freeze_min_age parameters that are larger than half the system-wide autovacuum_freeze_max_age setting.
- autovacuum_freeze_max_age , toast.autovacuum_freeze_max_age ( integer )
-
Per-table value for autovacuum_freeze_max_age parameter. Note that autovacuum will ignore per-table autovacuum_freeze_max_age parameters that are larger than the system-wide setting (it can only be set smaller).
- autovacuum_freeze_table_age , toast.autovacuum_freeze_table_age ( integer )
-
Per-table value for vacuum_freeze_table_age parameter.
- autovacuum_multixact_freeze_min_age , toast.autovacuum_multixact_freeze_min_age ( integer )
-
Per-table value for vacuum_multixact_freeze_min_age parameter. Note that autovacuum will ignore per-table autovacuum_multixact_freeze_min_age parameters that are larger than half the system-wide autovacuum_multixact_freeze_max_age setting.
- autovacuum_multixact_freeze_max_age , toast.autovacuum_multixact_freeze_max_age ( integer )
-
Per-table value for autovacuum_multixact_freeze_max_age parameter. Note that autovacuum will ignore per-table autovacuum_multixact_freeze_max_age parameters that are larger than the system-wide setting (it can only be set smaller).
- autovacuum_multixact_freeze_table_age , toast.autovacuum_multixact_freeze_table_age ( integer )
-
Per-table value for vacuum_multixact_freeze_table_age parameter.
- log_autovacuum_min_duration , toast.log_autovacuum_min_duration ( integer )
-
Per-table value for log_autovacuum_min_duration parameter.
- user_catalog_table ( boolean )
-
Declare the table as an additional catalog table for purposes of logical replication. See Section 47.6.2 for details. This parameter cannot be set for TOAST tables.
Notes
Using OIDs in new applications is not recommended: where possible, using a SERIAL or other sequence generator as the table's primary key is preferred. However, if your application does make 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.
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.
PostgreSQL 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 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)
);
Assign a literal constant default value for the column name , arrange for the default value of column did to be generated by selecting the next value of a sequence object, and make 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 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 serial,
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. 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 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 PostgreSQL does not support SQL modules, this distinction is not relevant in PostgreSQL .
For compatibility's sake, PostgreSQL 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 PostgreSQL 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 PostgreSQL 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, PostgreSQL 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. 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. SQL:1999 and later define single inheritance using a different syntax and different semantics. SQL:1999-style inheritance is not yet supported by PostgreSQL .
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.
LIKE Clause
While a LIKE clause exists in the SQL standard, many of the options that PostgreSQL accepts for it are not in the standard, and some of the standard's options are not implemented by PostgreSQL .
WITH Clause
The WITH clause is a PostgreSQL extension; neither storage parameters nor OIDs are in the standard.
Tablespaces
The PostgreSQL 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" . PostgreSQL does not support these self-referencing columns explicitly, but the same effect can be had using the OID feature.