CREATE TABLE

版本:11

CREATE TABLE — 定義一個新的資料表

語法

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 [, ... ] ) ]
[ PARTITION BY { RANGE | LIST } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ 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 }
[, ... ]
) ]
[ PARTITION BY { RANGE | LIST } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ 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
PARTITION OF parent_table [ (
{ column_name [ WITH OPTIONS ] [ column_constraint [ ... ] ]
| table_constraint }
[, ... ]
) ] FOR VALUES partition_bound_spec
[ PARTITION BY { RANGE | LIST } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ 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 |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
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 | IDENTITY | INDEXES | STORAGE | COMMENTS | ALL }
and partition_bound_spec is:
IN ( { numeric_literal | string_literal | NULL } [, ...] ) |
FROM ( { numeric_literal | string_literal | MINVALUE | MAXVALUE } [, ...] )
TO ( { numeric_literal | string_literal | MINVALUE | MAXVALUE } [, ...] )
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 } ]

說明

CREATE TABLE 將在目前資料庫中建立一個新的,初始化為空的資料表。該資料表將由發出此指令的使用者擁有。

如果加上了綱要名稱(例如,CREATE TABLE myschema.mytable ...),那麼將在指定的綱要中建立資料表。否則,它將在目前綱要中建立。臨時資料表存在於特殊綱要中,因此在建立臨時資料表時無法使用綱要名稱。資料表的名稱必須與同一綱要中的任何其他資料表、序列、索引、檢視表或外部資料表的名稱不同。

CREATE TABLE 還自動建立一個資料型別,表示與資料表的一個資料列對應的複合型別。因此,資料表不能與同一綱要中的任何現有資料型別具有相同的名稱。

可選擇性加上限制條件子句指定新的資料列或更新資料列必須滿足的限制條件才能使其插入或更新操作成功。限制條件是一個 SQL 物件,它有助於以各種方式定義資料表中的有效值集合。

定義限制條件有兩種方法:資料表限制條件和欄位限制條件。欄位限制條件被定義為欄位定義的一部分。資料表限制條件定義不依賴於特定欄位,它可以包含多個欄位。 每個欄位限制條件也可以寫為資料表限制條件;欄位限制條件只是在其限制僅影響一欄位時使用的語法方便。

為了能夠建立資料表,您必須分別對所有欄位型別或 OF 子句中的型別具有 USAGE 權限。

參數

TEMPORARYTEMP

如果使用此參數,則將資料表建立為臨時資料表。臨時資料表會在連線結束時自動刪除,或者選擇性地在目前交易事務結束時刪除(請參閱下面的 ON COMMIT)。當臨時資料表存在時,目前連線不會顯示具有相同名稱的現有永久資料表,除非它們使用綱要限定的名稱引用。在臨時資料表上建立的任何索引也都自動是臨時的。

由於 autovacuum 背景程序無法存取,因此無法對臨時資料表進行清理或分析。所以,應透過線上的 SQL 命令執行適當的清理和分析操作。例如,如果要在複雜查詢中使用臨時資料表,在填入資料後的臨時表上執行 ANALYZE 是個不錯的作法。

選擇性地,可以在 TEMPORARY 或 TEMP 之前寫入 GLOBAL 或 LOCAL。目前這在 PostgreSQL 中沒有任何區別,也已經被棄用;請參閱相容性

UNLOGGED

如果指定了這個選項,則將此表建立為無日誌記錄的資料表。寫入無日誌記錄資料表的資料不寫入 WAL(見第 30 章),這使得它們比普通的資料表快得多。但是,它們就不是完全安全的:在系統崩潰或不正常關閉之後,會自動清除無日誌記錄的資料表。 無日誌記錄的資料表內容也無法複製到備用伺服器。在無日誌記錄資料表上所建的所有索引也沒有日誌記錄。

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.

PARTITION OF parent_table FOR VALUES partition_bound_spec

Creates the table as a partition of the specified parent table.

The partition_bound_spec must correspond to the partitioning method and partition key of the parent table, and must not overlap with any existing partition of that parent. The form with IN is used for list partitioning, while the form with FROM and TO is used for range partitioning.

Each of the values specified in the partition_bound_spec is a literal, NULL, MINVALUE, or MAXVALUE. Each literal value must be either a numeric constant that is coercible to the corresponding partition key column's type, or a string literal that is valid input for that type.

When creating a list partition, NULL can be specified to signify that the partition allows the partition key column to be null. However, there cannot be more than one such list partition for a given parent table. NULL cannot be specified for range partitions.

When creating a range partition, the lower bound specified with FROM is an inclusive bound, whereas the upper bound specified with TO is an exclusive bound. That is, the values specified in the FROM list are valid values of the corresponding partition key columns for this partition, whereas those in the TO list are not. Note that this statement must be understood according to the rules of row-wise comparison (Section 9.23.5). For example, given PARTITION BY RANGE (x,y), a partition bound FROM (1, 2) TO (3, 4) allows x=1 with anyy>=2, x=2 with any non-null y, and x=3 with any y<4.

The special values MINVALUE and MAXVALUE may be used when creating a range partition to indicate that there is no lower or upper bound on the column's value. For example, a partition defined using FROM (MINVALUE) TO (10) allows any values less than 10, and a partition defined using FROM (10) TO (MAXVALUE) allows any values greater than or equal to 10.

When creating a range partition involving more than one column, it can also make sense to use MAXVALUE as part of the lower bound, and MINVALUE as part of the upper bound. For example, a partition defined using FROM (0, MAXVALUE) TO (10, MAXVALUE) allows any rows where the first partition key column is greater than 0 and less than or equal to 10. Similarly, a partition defined using FROM ('a', MINVALUE) TO ('b', MINVALUE) allows any rows where the first partition key column starts with "a".

Note that if MINVALUE or MAXVALUE is used for one column of a partitioning bound, the same value must be used for all subsequent columns. For example, (10, MINVALUE, 0) is not a valid bound; you should write (10, MINVALUE, MINVALUE).

Also note that some element types, such as timestamp, have a notion of "infinity", which is just another value that can be stored. This is different from MINVALUE and MAXVALUE, which are not real values that can be stored, but rather they are ways of saying that the value is unbounded. MAXVALUE can be thought of as being greater than any other value, including "infinity" and MINVALUE as being less than any other value, including "minus infinity". Thus the range FROM ('infinity') TO (MAXVALUE) is not an empty range; it allows precisely one value to be stored — "infinity".

A partition must have the same column names and types as the partitioned table to which it belongs. If the parent is specified WITH OIDS then all partitions must have OIDs; the parent's OID column will be inherited by all partitions just like any other column. Modifications to the column names or types of a partitioned table, or the addition or removal of an OID column, will automatically propagate to all partitions. CHECK constraints will be inherited automatically by every partition, but an individual partition may specify additional CHECK constraints; additional constraints with the same name and condition as in the parent will be merged with the parent constraint. Defaults may be specified separately for each partition.

Rows inserted into a partitioned table will be automatically routed to the correct partition. If no suitable partition exists, an error will occur. Also, if updating a row in a given partition would require it to move to another partition due to new partition key values, an error will occur.

Operations such as TRUNCATE which normally affect a table and all of its inheritance children will cascade to all partitions, but may also be performed on an individual partition. Note that dropping a partition with DROP TABLE requires taking an ACCESS EXCLUSIVE lock on the parent table.

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.

If a column in the parent table is an identity column, that property is not inherited. A column in the child table can be declared identity column if desired.

PARTITION BY { RANGE | LIST } ( { column_name | ( expression ) } [ opclass ] [, ...] )

The optional PARTITION BY clause specifies a strategy of partitioning the table. The table thus created is called a partitioned table. The parenthesized list of columns or expressions forms the partition key for the table. When using range partitioning, the partition key can include multiple columns or expressions (up to 32, but this limit can be altered when building PostgreSQL), but for list partitioning, the partition key must consist of a single column or expression. If no B-tree operator class is specified when creating a partitioned table, the default B-tree operator class for the datatype will be used. If there is none, an error will be reported.

A partitioned table is divided into sub-tables (called partitions), which are created using separate CREATE TABLE commands. The partitioned table is itself empty. A data row inserted into the table is routed to a partition based on the value of columns or expressions in the partition key. If no existing partition matches the values in the new row, an error will be reported.

Partitioned tables do not support UNIQUE, PRIMARY KEY, EXCLUDE, or FOREIGN KEY constraints; however, you can define these constraints on individual partitions.

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.

Any identity specifications of copied column definitions will only be copied if INCLUDING IDENTITY is specified. A new sequence is created for each identity column of the new table, separate from the sequences associated with the old table.

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 STORAGEsettings, see Section 66.2.

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 IDENTITY 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. 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.

GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]

This clause creates the column as an identity column. It will have an implicit sequence attached to it and the column in new rows will automatically have values from the sequence assigned to it.

The clauses ALWAYS and BY DEFAULT determine how the sequence value is given precedence over a user-specified value in an INSERT statement. If ALWAYS is specified, a user-specified value is only accepted if the INSERT statement specifies OVERRIDING SYSTEM VALUE. If BY DEFAULT is specified, then the user-specified value takes precedence. See INSERT for details. (In the COPY command, user-specified values are always used regardless of this setting.)

The optional sequence_options clause can be used to override the options of the sequence. See CREATE SEQUENCE for details.

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.

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. 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, but 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.

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_elementcan optionally specify an operator class and/or ordering options; these are described fully under CREATE INDEX.

The access method must support amgettuple (see Chapter 60); 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. The user must have REFERENCES permission on the referenced table (either the whole table, or the specific referenced columns). 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 ACTIONcheck 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 CONSTRAINTScommand). 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

tablespace_name 是要在其中建立新資料表的資料表空間名稱。如果未指定,則會使用 default_tablespace,如果此資料表是臨時資料表,則為使用 temp_tablespaces

USING INDEX TABLESPACE tablespace_name

此子句允許選擇與其建立的 UNIQUE,PRIMARY KEY 或 EXCLUDE 限制條件約束關連索引的資料表空間。如果未指定,則使用 default_tablespace,如果此表是臨時資料表,則為 temp_tablespaces

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 66.2 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. Specifying these parameters for partitioned tables is not supported, but you may specify them for individual leaf partitions.

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 (float4)

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 (float4)

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 48.6.2 for details. This parameter cannot be set for TOAST tables.

Notes

Using OIDs in new applications is not recommended: where possible, using an identity column 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.)

範例

建立資料表 flims 和資料表 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 GENERATED BY DEFAULT AS IDENTITY,
name varchar(40) NOT NULL CHECK (name <> '')
);

建立一個包含二維陣列的資料表:

CREATE TABLE array_int (
vector int[][]
);

為資料表 films 定義唯一性的資料表限制條件。可以在資料表的一個欄位或多個欄位上定義唯一性的資料表限制條件:

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)
);

定義檢查欄位的限制條件:

CREATE TABLE distributors (
did integer CHECK (did > 100),
name varchar(40)
);

定義 CHECK 資料表限制條件:

CREATE TABLE distributors (
did integer,
name varchar(40),
CONSTRAINT con1 CHECK (did > 100 AND name <> '')
);

為資料表 films 定義主鍵的資料表限制條件:

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)
);

為資料表 distributors 定義主鍵限制條件。以下兩個範例是等效的,第一個使用資料表限制條件語法,第二個是欄位限制條件語法:

CREATE TABLE distributors (
did integer,
name varchar(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did integer PRIMARY KEY,
name varchar(40)
);

為欄位名稱指定文字常數預設值,透過以序列物件的下一個值來安排要産生的欄位預設值,並使預設值 modtime 成為插入資料列的時間:

CREATE TABLE distributors (
name varchar(40) DEFAULT 'Luso Films',
did integer DEFAULT nextval('distributors_serial'),
modtime timestamp DEFAULT current_timestamp
);

在資料表 distributors 上定義兩個 NOT NULL 欄位限制條件,其中一個明確地設定了名稱:

CREATE TABLE distributors (
did integer CONSTRAINT no_null NOT NULL,
name varchar(40) NOT NULL
);

為 name 欄位定義唯一性限制條件:

CREATE TABLE distributors (
did integer,
name varchar(40) UNIQUE
);

同樣,但指定為資料表限制條件:

CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name)
);

建立相同的資料表,為資料表及其唯一性索引指定 70% 填充因子:

CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name) WITH (fillfactor=70)
)
WITH (fillfactor=70);

使用排除限制條件建立資料表 circles,以防止任何兩個 circle 重疊:

CREATE TABLE circles (
c circle,
EXCLUDE USING gist (c WITH &&)
);

在資料表空間 diskvol1 中建立資料表 cinemas:

CREATE TABLE cinemas (
id serial,
name text,
location text
) TABLESPACE diskvol1;

建立複合型別和該型別的資料表:

CREATE TYPE employee_type AS (name text, salary numeric);
CREATE TABLE employees OF employee_type (
PRIMARY KEY (name),
salary WITH OPTIONS DEFAULT 1000
);

建立區間型的分割資料表:

CREATE TABLE measurement (
logdate date not null,
peaktemp int,
unitsales int
) PARTITION BY RANGE (logdate);

在分割主鍵中建立一個包含多個欄位的區間分割資料表:

CREATE TABLE measurement_year_month (
logdate date not null,
peaktemp int,
unitsales int
) PARTITION BY RANGE (EXTRACT(YEAR FROM logdate), EXTRACT(MONTH FROM logdate));

建立列表型分割資料表:

CREATE TABLE cities (
city_id bigserial not null,
name text not null,
population bigint
) PARTITION BY LIST (left(lower(name), 1));

建立區間型分割資料表的分割區:

CREATE TABLE measurement_y2016m07
PARTITION OF measurement (
unitsales DEFAULT 0
) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');

在分割主鍵中建立具有多個欄位的區間型分割資料表的幾個分割區:

CREATE TABLE measurement_ym_older
PARTITION OF measurement_year_month
FOR VALUES FROM (MINVALUE, MINVALUE) TO (2016, 11);
CREATE TABLE measurement_ym_y2016m11
PARTITION OF measurement_year_month
FOR VALUES FROM (2016, 11) TO (2016, 12);
CREATE TABLE measurement_ym_y2016m12
PARTITION OF measurement_year_month
FOR VALUES FROM (2016, 12) TO (2017, 01);
CREATE TABLE measurement_ym_y2017m01
PARTITION OF measurement_year_month
FOR VALUES FROM (2017, 01) TO (2017, 02);

建立列表分割資料表的分割區:

CREATE TABLE cities_ab
PARTITION OF cities (
CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b');

建立列表型分割資料表的分割區,該資料表本身進一步進行分區,然後向其加上分割區:

CREATE TABLE cities_ab
PARTITION OF cities (
CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b') PARTITION BY RANGE (population);
CREATE TABLE cities_ab_10000_to_100000
PARTITION OF cities_ab FOR VALUES FROM (10000) TO (100000);

相容性

CREATE TABLE 命令基本上符合 SQL 標準,而下面列出了一些例外情況。

Temporary Tables

儘管 CREATE TEMPORARY TABLE 的語法類似於 SQL 標準的語法,但效果卻不盡相同。在標準中,臨時資料表只定義一次,並在每個需要它們的連線中自動存在(以空內容開始)。 而 PostgreSQL 則要求每個連線為要使用的每個臨時資料表發出自己的 CREATE TEMPORARY TABLE 命令。這使得不同的連線可以為不同的目的使用相同的臨時資料表名稱,而標準的方法限制了給定臨時資料表名稱的所有物件具有相同的資料表結構。

標準對臨時資料表行為的定義大部份都被忽略。PostgreSQL 在這一點上的行為類似於其他幾個 SQL 資料庫。

SQL 標準還區分全域和區域的臨時資料表,其中區域的臨時資料表為每個連線中的每個 SQL 區塊都有一組單獨的內容,儘管它的定義仍然在連線之間共享。由於 PostgreSQL 不支援 SQL 區塊,因此這種區別與 PostgreSQL 無關。

為了相容性,PostgreSQL 將在臨時資料表宣告中接受 GLOBAL 和 LOCAL 關鍵字,但它們目前沒有任何效果。並不鼓勵使用這些關鍵字,因為 PostgreSQL 的未來版本可能採用更符合標準的方式來解譯。

臨時資料表的 ON COMMIT 子句也類似於 SQL 標準,但有一些差異。 如果省略 ON COMMIT 子句,則 SQL 指定預設行為為 ON COMMIT DELETE ROWS。但是,PostgreSQL 中的預設行為是 ON COMMIT PRESERVE ROWS。SQL 中不存在 ON COMMIT DROP 語法。

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.

EXCLUDE Constraint

The EXCLUDE constraint type is a PostgreSQL extension.

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.

Multiple Identity Columns

PostgreSQL allows a table to have more than one identity column. The standard specifies that a table can have at most one identity column. This is relaxed mainly to give more flexibility for doing schema changes or migrations. Note that the INSERT command supports only one override clause that applies to the entire statement, so having multiple identity columns with different behaviors is not well supported.

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.

PARTITION BY Clause

The PARTITION BY clause is a PostgreSQL extension.

參閱

ALTER TABLE, DROP TABLE, CREATE TABLE AS, CREATE TABLESPACE, CREATE TYPE