CREATE [ [ LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name (
{ column_name data_type [ DEFAULT default_expr ] [ column_constraint [, ... ] ]
| table_constraint } [, ... ]
)
[ INHERITS ( parent_table [, ... ] ) ]
[ WITH OIDS | WITHOUT OIDS ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | UNIQUE | PRIMARY KEY |
CHECK (expression) |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL ]
[ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint is:
[ CONSTRAINT constraint_name ]
{ UNIQUE ( column_name [, ... ] ) |
PRIMARY KEY ( column_name [, ... ] ) |
CHECK ( expression ) |
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL ] [ ON DELETE action ] [ ON UPDATE action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
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 (the one at the front of the search path; see CURRENT_SCHEMA()). TEMP tables exist in a special schema, so a schema name may not be given when creating a TEMP table. The table name must be distinct from the name of any other table, sequence, index, or view in the same schema.
CREATE TABLE also automatically creates a data type that represents the tuple type (structure type) corresponding to one row of the table. Therefore, tables cannot have the same name as any existing data type in the same schema.
A table cannot have more than 1600 columns. (In practice, the effective limit is lower because of tuple-length constraints).
The optional constraint clauses specify constraints (or tests) that new or updated rows must satisfy for an insert or update operation to succeed. A constraint is a named rule: an SQL object which helps define valid sets of values by putting limits on the results of insert, update, or delete operations performed on a table.
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 if the constraint only affects one column.
If specified, the table is created as a temporary table. Temporary tables are automatically dropped at the end of a session. 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 LOCAL word is optional. But see under Compatibility.
The name (optionally schema-qualified) of the table to be created.
The name of a column to be created in the new table.
The data type of the column. This may include array specifiers. Refer to the User's Guide for further information about data types and arrays.
The DEFAULT clause assigns a default data value for the column whose column definition it appears within. The value is any variable-free expression (subselects 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.
The optional INHERITS clause specifies a list of tables from which the new table automatically inherits all columns. 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 that is also inherited, the data type must likewise match the inherited column(s), and the column definitions are merged into one. However, inherited and new column declarations of the same name need not specify identical constraints: all constraints provided from any declaration are merged together and all are applied to the new table. If the new table explicitly specifies a default value for the column, this default overrides any defaults from inherited declarations of the column. Otherwise, any parents that specify default values for the column must all specify the same default, or an error will be reported.
This optional clause specifies whether rows of the new table should have OIDs (object identifiers) assigned to them. The default is to have OIDs. (If the new table inherits from any tables that have OIDs, then WITH OIDS is forced even if the command says WITHOUT OIDS.)
Specifying WITHOUT OIDS allows the user to suppress generation of OIDs for rows of a table. This may be worthwhile for large tables, since it will reduce OID consumption and thereby postpone wraparound of the 32-bit OID counter. Once the counter wraps around, uniqueness of OIDs can no longer be assumed, which considerably reduces their usefulness.
An optional name for a column or table constraint. If not specified, the system generates a name.
The column is not allowed to contain NULL values.
The column is allowed to contain NULL values. This is the default.
This clause is only available for compatibility with non-standard SQL databases. Its use is discouraged in new applications.
The UNIQUE constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique values. The behavior of the unique table constraint is the same as that for column constraints, with the additional capability to span multiple columns.
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.)
The primary key constraint specifies that a column or columns of a table may contain only unique (non-duplicate), non-NULL values. Technically, PRIMARY KEY is merely a combination of UNIQUE and NOT NULL, but identifying a set of columns as primary key also provides meta-data about the design of the schema, as a primary key implies that other tables may rely on this set of columns as a unique identifier for rows.
Only one primary key can be specified for a table, whether as a column constraint or a table constraint.
The primary key constraint should name a set of columns that is different from other sets of columns named by any unique constraint defined for the same table.
CHECK clauses specify integrity constraints or tests which new or updated rows must satisfy for an insert or update operation to succeed. Each constraint must be an expression producing a Boolean result. A condition appearing within a column definition should reference that column's value only, while a condition appearing as a table constraint may reference multiple columns.
Currently, CHECK expressions cannot contain subselects nor refer to variables other than columns of the current row.
The REFERENCES column constraint specifies that a group of one or more columns of the new table must only contain values which match against values in the referenced column(s) refcolumn of the referenced table reftable. If refcolumn is omitted, the primary key of the reftable is used. The referenced columns must be the columns of a unique or primary key constraint in the referenced table.
A value added to these columns 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 a default match type if none is specified. MATCH FULL will not allow one column of a multicolumn foreign key to be NULL unless all foreign key columns are NULL. The default match type 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 do 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. There are the following possible actions for each clause:
Produce an error indicating that the deletion or update would create a foreign key constraint violation. This is the default action.
Same as NO ACTION.
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 the referencing column values to NULL.
Set the referencing column values to their default value.
If primary key column is updated frequently, it may be wise to add an index to the REFERENCES column so that NO ACTION and CASCADE actions associated with the REFERENCES column can be more efficiently performed.
This controls whether the constraint can be deferred. A constraint that is not deferrable will be checked immediately after every command. Checking of constraints that are deferrable may be postponed until the end of the transaction (using the SET CONSTRAINTS command). NOT DEFERRABLE is the default. Only foreign key constraints currently accept this clause. All other constraint types are not deferrable.
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