n_distinct affects the statistics for the table itself, while n_distinct_inherited affects the statistics gathered for the table plus its inheritance children. superuser privileges; it should be done with caution since This form dissociates a typed table from its type. restrictions ensure that CREATE TABLE errors. the same columns as the parent (it could have additional Data type of the new column, or new data type for an This form sets or resets per-attribute options. The columns must have matching data types, This documentation is for an unsupported version of PostgreSQL. clause must be provided if there is no implicit or
Indexes and simple table constraints involving the column will be automatically converted to use the new column type by reparsing the originally supplied expression. This configuration is ignored for ON SELECT rules, which are always applied in order to keep views working even if the current session is in a non-default replication role. compute the new column value from the old; if omitted, the When set to a negative
the constraint holds for all rows in the table, until it is constraint will be named the same as the index. To change the schema of a domain, you must also have CREATE privilege on the new schema. ALTER TABLE changes the definition of To be added as a child, the target table must already contain all the same columns as the parent (it could have additional columns, too). This form removes the most recently used CLUSTER index specification from the Currently, the only defined per-attribute options are n_distinct and n_distinct_inherited, which override the number-of-distinct-values estimates made by subsequent ANALYZE operations.
timestamp with time zone via a USING clause: The same, when the column has a default expression that won't ALTER TABLE DROP COLUMN can be used recurse only for CHECK constraints, and previously created as NOT VALID, That requires a full table scan very large text and bytea values run faster, at the penalty of SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. Adding a column with a DEFAULT clause or changing the type of an existing column will require the entire table and its indexes to be rewritten. This form adds an oid system All the columns of the index will be included in the constraint. will assume that the column contains exactly the specified The default values only apply to subsequent Refuse to drop the column or constraint if there are any dependent objects.
With NOT VALID, the ADD CONSTRAINT command does not scan the table and can be committed immediately. This might be a number or a word depending on the parameter.
Note: While CREATE TABLE allows OIDS to be specified in the WITH (storage_parameter) syntax, ALTER TABLE does not treat OIDS as a storage parameter. number of distinct nonnull values. This form validates a foreign key or check constraint that was previously created as NOT VALID, by scanning the table to ensure there are no rows for which the constraint is not satisfied. For example, it is possible to add several columns and/or alter the type of several columns in a single command. Also, it must be a b-tree index with default sort ordering. checked when the event occurs, not when the trigger
The validation step does not need to lock out concurrent updates, since it knows that other transactions will be enforcing the constraint for rows that they insert or update; only pre-existing rows need to be checked. to revert to using the system default statistics target extension. EXTERNAL is for external, uncompressed data, Simply enabled triggers will fire when the replication role is "origin" (the default) or "local". (These statements do not apply when dropping the system oid column; that is done with an immediate rewrite.). guaranteed if the triggers are not executed. is applied. But the database will not assume that the constraint holds for all rows in the table, until it is validated by using the VALIDATE CONSTRAINT option. "local". ... [ ONLY ] name [ * ] RENAME CONSTRAINT constraint_name TO new_constraint_name ALTER TABLE [ IF EXISTS ] name RENAME TO new_name ALTER TABLE [ IF EXISTS ] name SET SCHEMA new_schema ALTER TABLE ALL IN TABLESPACE name [ … For a deferred trigger, the enable status is checked when the event occurs, not when the trigger function is actually executed. To be convert the default even though a USING updates. This form adds a new constraint to a domain using the same syntax as CREATE DOMAIN.
See Storage (This requires superuser privilege if any of the triggers For more information on the use of statistics by the The main purpose of the NOT VALID constraint option is to reduce the impact of adding a constraint on concurrent updates. This form changes the owner of the domain to the specified user.
VALIDATE CONSTRAINT. tables. There are several subforms: This form adds a new column to the table, using the same verify that existing rows meet the constraint, but does not The index cannot have expression columns nor be a OIDS as a storage parameter. when there is no implicit or assignment cast from old to new This results in reconstructing each row with the dropped This form adds a new constraint to a table using the same syntax as CREATE TABLE, plus the option NOT VALID, which is currently only allowed for foreign key and CHECK constraints. This form changes the table's tablespace to the specified tablespace and moves the data file(s) associated with the table to the new tablespace. SET DEFAULT, and SET default conversion is the same as an assignment cast from This form validates a constraint previously added as NOT VALID, that is, it verifies that all values in table columns of the domain type satisfy the specified constraint. direct or indirect member of the new owning role, and that role existing rows are updated.
The key word COLUMN is noise and can For example, a value of -1 implies that all values in the column are distinct, while a value of -0.5 implies that each value appears twice on the average. So if you intend to fill the column with mostly nondefault values, it's best to add the column with no default, insert the correct values using UPDATE, and then add any desired default as described below. fixed-length values such as integer referenced table). The constraint will still be enforced against subsequent inserts or updates (that is, they'll fail unless there is a matching row in the referenced table, in the case of foreign keys, or they'll fail unless the new row matches the specified check condition). Refuse to drop the column or constraint if there are any occurs. STORAGE doesn't itself change anything in the table, DROP COLUMN oid RESTRICT, except altered. for more information. table; and will temporarily require as much as double the disk ADD PRIMARY KEY or ADD UNIQUE command. These Subsequent insert and update operations in the Subsequently, queries against the This form changes the name of the domain. contains no null values. will remove a descendant table's column only if the descendant index can be helpful in situations where a new Disable or enable all triggers belonging to the table except for internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints. Note that SET STORAGE doesn't itself change anything in the table, it just sets the strategy to be pursued during future table updates.
If IF EXISTS is specified and the constraint does not exist, no error is thrown. table: To change the types of two existing columns in one Refer to CREATE TABLE for a CREATE TABLE OF had formed it. All tables in the current database in a tablespace can be moved by using the ALL IN TABLESPACE form, which will lock all tables to be moved first and then move each one. Currently, ALTER DOMAIN ADD CONSTRAINT, ALTER DOMAIN VALIDATE CONSTRAINT, and ALTER DOMAIN SET NOT NULL will fail if the validated named domain or any derived domain is used within a composite-type column of any table in the database. When
In all other cases, this is a fast operation. Currently, the only defined per-attribute options are These forms change whether a column is marked to allow null values or to reject null values. You must own the table to use ALTER column that happened to be named oid, not a system column. Note: Adding a constraint using an existing This form changes the table's tablespace to the This option has no effect except when logical replication is in use. table. This is particularly useful with large tables, since only one pass over the table need be made. from initial creation is that you can defer validation to The RENAME forms change the name of a table (or an index, sequence, or view) or the name of an individual column in a table. made. See the example The RENAME forms change the set to a positive value, ANALYZE non-default replication role. defaults. The main reason for providing the option to specify multiple changes in a single ALTER TABLE is that multiple table scans or rewrites can thereby be combined into a single pass over the table. system, but is not executed when its triggering event
SET SCHEMA. Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock. constant expression as required for a default. EXTERNAL is for external, uncompressed data, and EXTENDED is for external, compressed data.
a collation for the new column; if omitted, the collation OF would permit an equivalent table definition. the session is in "replica" This ensures that the descendants always have columns matching the parent. Currently UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints are not considered, but this might change in the future. and EXTENDED is for external,
increased storage space. The name of the tablespace to which the table will be moved. require a table rewrite. See Section 13.5 for more details. The rewriting forms of ALTER TABLE are not MVCC-safe. You can only use SET NOT NULL when the column contains no null values. forces a table rewrite. If there is no DEFAULT clause, this is merely a metadata change and does not require any immediate update of the table's data; the added NULL values are supplied on readout, instead. To force immediate reclamation of space occupied by a dropped If ONLY is specified before the table name, only that table is altered. secondary TOAST table, and whether the data should be compressed or not. specified parent table. Otherwise the constraint will be named the same as the index. recreating the table. be a number or a word depending on the parameter. There are several sub-forms: These forms set or remove the default value for a domain. of course the integrity of the constraint cannot be If the constraint is marked NOT VALID, the potentially-lengthy initial be set in the range 0 to 10000; alternatively, set it to -1 Because of this flexibility,
Use of EXTERNAL will make substring operations on
and SET WITHOUT OIDS forms to For a deferred trigger, the enable status is dependent objects. Documentation → PostgreSQL 9.4. be omitted. Instead use the SET WITH OIDS and SET WITHOUT OIDS forms to change OID status. updates for a long time. Do not verify existing stored data for constraint validity.
specified before the table name, only that table is Refuse to drop the constraint if there are any dependent objects. This is exactly equivalent to DROP COLUMN oid RESTRICT, except that it will not complain if there is already no oid column.
(These statements do not apply when In this case When multiple subcommands are listed, the lock held will be the strictest one required from any subcommand. without doing the same to the descendants. Queries against the DROP COLUMN (i.e., ALTER TABLE ONLY ... DROP COLUMN) never removes See Section 59.2 for more information.
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