CREATE TABLE SQL - Language Statements CREATE TABLE define a new table CREATE TABLE CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE table_name ( { column_name data_type [ DEFAULT default_expr ] [ column_constraint [ ... ] ] | table_constraint | LIKE parent_table [ { INCLUDING | EXCLUDING } DEFAULTS ] } [, ... ] ) [ INHERITS ( parent_table [, ... ] ) ] [ WITH OIDS | WITHOUT OIDS ] [ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ] where column_constraint is: [ CONSTRAINT constraint_name ] { NOT NULL | NULL | UNIQUE | PRIMARY KEY | CHECK (expression) | 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 ] { UNIQUE ( column_name [, ... ] ) | PRIMARY KEY ( column_name [, ... ] ) | CHECK ( expression ) | 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 ] 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 may not be given when creating a temporary 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 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. 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 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 if the constraint only affects one column. 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. Optionally, GLOBAL or LOCAL can be written before TEMPORARY or TEMP. This makes no difference in PostgreSQL, but see . table_name The name (optionally schema-qualified) of the table to be created. column_name The name of a column to be created in the new table. data_type The data type of the column. This may include array specifiers. For more information on the data types included with PostgreSQL, refer to . 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. LIKE parent_table [ { INCLUDING | EXCLUDING } DEFAULTS ] The LIKE clause specifies a table from which the new table automatically inherits all column names, their data types, and not-null constraints. Unlike INHERITS, the new table and inherited table are complete decoupled after creation has been completed. Data inserted into the new table will not be reflected into the parent table. Default expressions for the inherited column definitions will only be included if INCLUDING DEFAULTS is specified. The default is to exclude default expressions. INHERITS ( parent_table [, ... ] ) 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. WITH OIDS WITHOUT OIDS This optional clause specifies whether rows of the new table should have OIDs (object identifiers) assigned to them. If neither WITH OIDS nor WITHOUT OIDS is specified, the default value depends upon the default_with_oids configuration parameter. (If the new table inherits from any tables that have OIDs, then WITH OIDS is forced even if the command says WITHOUT OIDS.) If WITHOUT OIDS is specified or implied, this means that the generation of OIDs for this table will be supressed. 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 on disk to storage the table by 4 bytes per row, leading to increased performance. To remove OIDs from a table after it has been created, use . CONSTRAINT constraint_name An optional name for a column or table constraint. If 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 available for compatibility with non-standard SQL databases. Its use is discouraged in new applications. UNIQUE (column constraint) UNIQUE ( column_name [, ... ] ) (table constraint) The UNIQUE constraint specifies 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.) PRIMARY KEY (column constraint) PRIMARY KEY ( column_name [, ... ] ) (table constraint) The primary key constraint specifies that a column or columns of a table may contain only unique (non-duplicate), nonnull values. Technically, PRIMARY KEY is merely a combination of UNIQUE and NOT NULL, but identifying a set of columns as primary key also provides metadata about the design of the schema, as a primary key implies that other tables may rely on this set of columns as a unique identifier for rows. Only one primary key can be specified for a table, whether as a column constraint or a table constraint. The primary key constraint should name a set of columns that is different from other sets of columns named by any unique constraint defined for the same table. CHECK (expression) 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. A check constraint specified as a column constraint should reference that column's value only, while an expression appearing in a table constraint may reference multiple columns. Currently, CHECK expressions cannot contain subqueries nor refer to variables other than columns of the current row. REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] (column constraint) FOREIGN KEY ( column [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ] [ MATCH matchtype ] [ ON DELETE action ] [ ON UPDATE action ] (table constraint) Theses clauses specify a foreign key constraint, which 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 inserted into 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 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. 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. This is the default action. RESTRICT Same as NO ACTION except that this action will not be deferred even if the rest of the constraint is deferrable and deferred. 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 values to null. SET DEFAULT 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 foreign key column so that NO ACTION and CASCADE actions associated with the foreign key column can be more efficiently performed. 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 may be postponed until the end of the transaction (using the command). NOT DEFERRABLE is the default. Only foreign key constraints currently accept this clause. All other constraint types 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 command. 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 is done at each commit. DROP The temporary table will be dropped at the end of the current transaction block. 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 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. The use of WITHOUT OIDS 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 the uniqueness. Thus, it is not necessary to create an explicit index for primary key columns. (See 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. 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 ( 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. Primary key 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 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 notation. CREATE TABLE distributors ( did integer, name varchar(40), PRIMARY KEY(did) ); CREATE TABLE distributors ( did integer PRIMARY KEY, name varchar(40) ); This assigns a literal constant default value for the column name, arranges for the default value of column did to be generated by selecting the next value of a sequence object, and makes 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 above is equivalent to the following specified as a table constraint: CREATE TABLE distributors ( did integer, name varchar(40), UNIQUE(name) ); The CREATE TABLE command conforms to SQL92 and to a subset of SQL99, with exceptions listed below. 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 standard's distinction between global and local temporary tables is not in PostgreSQL, since that distinction depends on the concept of modules, which PostgreSQL does not have. For compatibility's sake, PostgreSQL will accept the GLOBAL and LOCAL keywords in a temporary table declaration, but they have no effect. 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. The SQL standard says that CHECK column constraints may only refer to the column they apply to; only CHECK table constraints may refer to multiple columns. PostgreSQL does not enforce this restriction; it treats column and table check constraints alike. 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. Multiple inheritance via the INHERITS clause is a PostgreSQL language extension. SQL99 (but not SQL92) defines single inheritance using a different syntax and different semantics. SQL99-style inheritance is not yet supported by PostgreSQL. The PostgreSQL concept of OIDs is not standard. 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.