Serial Postgres Alter

• Postgres Serial Alter

ADD COLUMNThis form adds a new column to the table, using the same syntax as. DROP COLUMN IF EXISTS This form drops a column from a table. Indexes and table constraints involving the column will be automatically dropped as well. You will need to say CASCADE if anything outside the table depends on the column, for example, foreign key references or views. If IF EXISTS is specified and the column does not exist, no error is thrown. In this case a notice is issued instead. IF EXISTSDo not throw an error if the table does not exist.

A notice is issued in this case. SET DATA TYPEThis form changes the type of a column of a table. Indexes and simple table constraints involving the column will be automatically converted to use the new column type by reparsing the originally supplied expression.

The optional COLLATE clause specifies a collation for the new column; if omitted, the collation is the default for the new column type. The optional USING clause specifies how to compute the new column value from the old; if omitted, the default conversion is the same as an assignment cast from old data type to new. A USING clause must be provided if there is no implicit or assignment cast from old to new type. SET/ DROP DEFAULTThese forms set or remove the default value for a column.

Default values only apply in subsequent INSERT or UPDATE commands; they do not cause rows already in the table to change. SET/ DROP NOT NULLThese forms change whether a column is marked to allow null values or to reject null values. You can only use SET NOT NULL when the column contains no null values. SET STATISTICSThis form sets the per-column statistics-gathering target for subsequent operations. The target can be set in the range 0 to 10000; alternatively, set it to -1 to revert to using the system default statistics target. For more information on the use of statistics by the PostgreSQL query planner, refer to.SET STATISTICS acquires a SHARE UPDATE EXCLUSIVE lock. SET ( attributeoption = value.

)RESET ( attributeoption. )This form sets or resets per-attribute options. Currently, the only defined per-attribute options are ndistinct and ndistinctinherited, which override the number-of-distinct-values estimates made by subsequent operations.

Ndistinct affects the statistics for the table itself, while ndistinctinherited affects the statistics gathered for the table plus its inheritance children. When set to a positive value, ANALYZE will assume that the column contains exactly the specified number of distinct nonnull values. When set to a negative value, which must be greater than or equal to -1, ANALYZE will assume that the number of distinct nonnull values in the column is linear in the size of the table; the exact count is to be computed by multiplying the estimated table size by the absolute value of the given number. 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. This can be useful when the size of the table changes over time, since the multiplication by the number of rows in the table is not performed until query planning time. Specify a value of 0 to revert to estimating the number of distinct values normally.

Postgres Serial Alter

For more information on the use of statistics by the PostgreSQL query planner, refer to.Changing per-attribute options acquires a SHARE UPDATE EXCLUSIVE lock. SET STORAGEThis form sets the storage mode for a column. This controls whether this column is held inline or in a secondary TOAST table, and whether the data should be compressed or not. PLAIN must be used for fixed-length values such as integer and is inline, uncompressed. MAIN is for inline, compressible data. EXTERNAL is for external, uncompressed data, and EXTENDED is for external, compressed data.

EXTENDED is the default for most data types that support non- PLAIN storage. Use of EXTERNAL will make substring operations on very large text and bytea values run faster, at the penalty of increased storage space.

Note that SET STORAGE doesn't itself change anything in the table, it just sets the strategy to be pursued during future table updates. See for more information. ADD tableconstraint NOT VALID This form adds a new constraint to a table using the same syntax as, plus the option NOT VALID, which is currently only allowed for foreign key and CHECK constraints. If the constraint is marked NOT VALID, the potentially-lengthy initial check to verify that all rows in the table satisfy the constraint is skipped. 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; and they'll fail unless the new row matches the specified check constraints).

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. ADD tableconstraintusingindexThis form adds a new PRIMARY KEY or UNIQUE constraint to a table based on an existing unique index. All the columns of the index will be included in the constraint.The index cannot have expression columns nor be a partial index. Also, it must be a b-tree index with default sort ordering. These restrictions ensure that the index is equivalent to one that would be built by a regular ADD PRIMARY KEY or ADD UNIQUE command.If PRIMARY KEY is specified, and the index's columns are not already marked NOT NULL, then this command will attempt to do ALTER COLUMN SET NOT NULL against each such column.

That requires a full table scan to verify the column(s) contain no nulls. In all other cases, this is a fast operation.If a constraint name is provided then the index will be renamed to match the constraint name. Otherwise the constraint will be named the same as the index.After this command is executed, the index is 'owned' by the constraint, in the same way as if the index had been built by a regular ADD PRIMARY KEY or ADD UNIQUE command. In particular, dropping the constraint will make the index disappear too.

Note: Adding a constraint using an existing index can be helpful in situations where a new constraint needs to be added without blocking table updates for a long time. To do that, create the index using CREATE INDEX CONCURRENTLY, and then install it as an official constraint using this syntax. See the example below. ALTER CONSTRAINTThis form alters the attributes of a constraint that was previously created. Currently only foreign key constraints may be altered.

VALIDATE CONSTRAINTThis 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. Nothing happens if the constraint is already marked valid.Validation can be a long process on larger tables. The value of separating validation from initial creation is that you can defer validation to less busy times, or can be used to give additional time to correct pre-existing errors while preventing new errors. Note also that validation on its own does not prevent normal write commands against the table while it runs.Validation acquires only a SHARE UPDATE EXCLUSIVE lock on the table being altered. If the constraint is a foreign key then a ROW SHARE lock is also required on the table referenced by the constraint.

DROP CONSTRAINT IF EXISTS This form drops the specified constraint on a table. If IF EXISTS is specified and the constraint does not exist, no error is thrown. In this case a notice is issued instead. DISABLE/ ENABLE REPLICA ALWAYS TRIGGERThese forms configure the firing of trigger(s) belonging to the table. A disabled trigger is still known to the system, but is not executed when its triggering event occurs. For a deferred trigger, the enable status is checked when the event occurs, not when the trigger function is actually executed. One can disable or enable a single trigger specified by name, or all triggers on the table, or only user triggers (this option excludes internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints).

Disabling or enabling internally generated constraint triggers requires superuser privileges; it should be done with caution since of course the integrity of the constraint cannot be guaranteed if the triggers are not executed. The trigger firing mechanism is also affected by the configuration variable. Simply enabled triggers will fire when the replication role is 'origin' (the default) or 'local'. Triggers configured as ENABLE REPLICA will only fire if the session is in 'replica' mode, and triggers configured as ENABLE ALWAYS will fire regardless of the current replication mode. DISABLE/ ENABLE REPLICA ALWAYS RULEThese forms configure the firing of rewrite rules belonging to the table. A disabled rule is still known to the system, but is not applied during query rewriting. The semantics are as for disabled/enabled triggers.

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. CLUSTER ONThis form selects the default index for future operations. It does not actually re-cluster the table.Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock. SET WITHOUT CLUSTERThis form removes the most recently used index specification from the table.

This affects future cluster operations that don't specify an index.Changing cluster options acquires a SHARE UPDATE EXCLUSIVE lock. SET WITH OIDSThis form adds an oid system column to the table (see ). It does nothing if the table already has OIDs.Note that this is not equivalent to ADD COLUMN oid oid; that would add a normal column that happened to be named oid, not a system column. SET WITHOUT OIDSThis form removes the oid system column from the table. This is exactly equivalent to DROP COLUMN oid RESTRICT, except that it will not complain if there is already no oid column.

SET ( storageparameter = value. )This form changes one or more storage parameters for the table. See for details on the available parameters. Note that the table contents will not be modified immediately by this command; depending on the parameter you might need to rewrite the table to get the desired effects. That can be done with, or one of the forms of ALTER TABLE that forces a table rewrite. Note: While CREATE TABLE allows OIDS to be specified in the WITH ( storageparameter) syntax, ALTER TABLE does not treat OIDS as a storage parameter. Instead use the SET WITH OIDS and SET WITHOUT OIDS forms to change OID status.

RESET ( storageparameter. )This form resets one or more storage parameters to their defaults. As with SET, a table rewrite might be needed to update the table entirely. INHERIT parenttableThis form adds the target table as a new child of the specified parent table. Subsequently, queries against the parent will include records of the target table.

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). The columns must have matching data types, and if they have NOT NULL constraints in the parent then they must also have NOT NULL constraints in the child.There must also be matching child-table constraints for all CHECK constraints of the parent, except those marked non-inheritable (that is, created with ALTER TABLE. ADD CONSTRAINT. NO INHERIT) in the parent, which are ignored; all child-table constraints matched must not be marked non-inheritable. Currently UNIQUE, PRIMARY KEY, and FOREIGN KEY constraints are not considered, but this might change in the future. NO INHERIT parenttableThis form removes the target table from the list of children of the specified parent table.

Queries against the parent table will no longer include records drawn from the target table. OF typenameThis form links the table to a composite type as though CREATE TABLE OF had formed it. The table's list of column names and types must precisely match that of the composite type; the presence of an oid system column is permitted to differ. The table must not inherit from any other table.

These restrictions ensure that CREATE TABLE OF would permit an equivalent table definition. NOT OFThis form dissociates a typed table from its type. OWNERThis form changes the owner of the table, sequence, view, materialized view, or foreign table to the specified user. SET TABLESPACEThis form changes the table's tablespace to the specified tablespace and moves the data file(s) associated with the table to the new tablespace. Indexes on the table, if any, are not moved; but they can be moved separately with additional SET TABLESPACE commands. 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.

This form also supports OWNED BY, which will only move tables owned by the roles specified. If the NOWAIT option is specified then the command will fail if it is unable to acquire all of the locks required immediately.

Note that system catalogs are not moved by this command, use ALTER DATABASE or explicit ALTER TABLE invocations instead if desired. The informationschema relations are not considered part of the system catalogs and will be moved. REPLICA IDENTITYThis form changes the information which is written to the write-ahead log to identify rows which are updated or deleted. This option has no effect except when logical replication is in use. DEFAULT (the default for non-system tables) records the old values of the columns of the primary key, if any. USING INDEX records the old values of the columns covered by the named index, which must be unique, not partial, not deferrable, and include only columns marked NOT NULL. FULL records the old values of all columns in the row.

NOTHING records no information about the old row. (This is the default for system tables.) In all cases, no old values are logged unless at least one of the columns that would be logged differs between the old and new versions of the row. RENAMEThe RENAME forms change the name of a table (or an index, sequence, view, materialized view, or foreign table), the name of an individual column in a table, or the name of a constraint of the table. There is no effect on the stored data. SET SCHEMAThis form moves the table into another schema. Associated indexes, constraints, and sequences owned by table columns are moved as well.All the forms of ALTER TABLE that act on a single table, except RENAME, and SET SCHEMA can be combined into a list of multiple alterations to applied together.

For example, it is possible to add several columns and/or alter the type of several columns in a single command. This is particularly useful with large tables, since only one pass over the table need be made.You must own the table to use ALTER TABLE. To change the schema or tablespace of a table, you must also have CREATE privilege on the new schema or tablespace.

To add the table as a new child of a parent table, you must own the parent table as well. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have CREATE privilege on the table's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the table. However, a superuser can alter ownership of any table anyway.) To add a column or alter a column type or use the OF clause, you must also have USAGE privilege on the data type. NameThe name (optionally schema-qualified) of an existing table to alter.

If ONLY is specified before the table name, only that table is altered. If ONLY is not specified, the table and all its descendant tables (if any) are altered. Optionally,. can be specified after the table name to explicitly indicate that descendant tables are included.

ColumnnameName of a new or existing column. NewcolumnnameNew name for an existing column. NewnameNew name for the table. DatatypeData type of the new column, or new data type for an existing column. TableconstraintNew table constraint for the table. ConstraintnameName of a new or existing constraint. CASCADEAutomatically drop objects that depend on the dropped column or constraint (for example, views referencing the column).

RESTRICTRefuse to drop the column or constraint if there are any dependent objects. This is the default behavior. TriggernameName of a single trigger to disable or enable.

ALLDisable or enable all triggers belonging to the table. (This requires superuser privilege if any of the triggers are internally generated constraint triggers such as those that are used to implement foreign key constraints or deferrable uniqueness and exclusion constraints.) USERDisable 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.

IndexnameThe name of an existing index. StorageparameterThe name of a table storage parameter. ValueThe new value for a table storage parameter. This might be a number or a word depending on the parameter. ParenttableA parent table to associate or de-associate with this table. NewownerThe user name of the new owner of the table.

NewtablespaceThe name of the tablespace to which the table will be moved. NewschemaThe name of the schema to which the table will be moved. NotesThe key word COLUMN is noise and can be omitted.When a column is added with ADD COLUMN, all existing rows in the table are initialized with the column's default value (NULL if no DEFAULT clause is specified). 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.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. As an exception when changing the type of an existing column, if the USING clause does not change the column contents and the old type is either binary coercible to the new type or an unconstrained domain over the new type, a table rewrite is not needed; but any indexes on the affected columns must still be rebuilt. Adding or removing a system oid column also requires rewriting the entire table. Table and/or index rebuilds may take a significant amount of time for a large table; and will temporarily require as much as double the disk space.Adding a CHECK or NOT NULL constraint requires scanning the table to verify that existing rows meet the constraint, but does not require a table rewrite.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.The DROP COLUMN form does not physically remove the column, but simply makes it invisible to SQL operations.

Subsequent insert and update operations in the table will store a null value for the column. Thus, dropping a column is quick but it will not immediately reduce the on-disk size of your table, as the space occupied by the dropped column is not reclaimed. The space will be reclaimed over time as existing rows are updated. (These statements do not apply when dropping the system oid column; that is done with an immediate rewrite.)To force immediate reclamation of space occupied by a dropped column, you can execute one of the forms of ALTER TABLE that performs a rewrite of the whole table. This results in reconstructing each row with the dropped column replaced by a null value.The rewriting forms of ALTER TABLE are not MVCC-safe. After a table rewrite, the table will appear empty to concurrent transactions, if they are using a snapshot taken before the rewrite occurred.

See for more details.The USING option of SET DATA TYPE can actually specify any expression involving the old values of the row; that is, it can refer to other columns as well as the one being converted. This allows very general conversions to be done with the SET DATA TYPE syntax. Because of this flexibility, the USING expression is not applied to the column's default value (if any); the result might not be a constant expression as required for a default. This means that when there is no implicit or assignment cast from old to new type, SET DATA TYPE might fail to convert the default even though a USING clause is supplied. In such cases, drop the default with DROP DEFAULT, perform the ALTER TYPE, and then use SET DEFAULT to add a suitable new default. Similar considerations apply to indexes and constraints involving the column.If a table has any descendant tables, it is not permitted to add, rename, or change the type of a column, or rename an inherited constraint in the parent table without doing the same to the descendants. That is, ALTER TABLE ONLY will be rejected.

This ensures that the descendants always have columns matching the parent.A recursive DROP COLUMN operation will remove a descendant table's column only if the descendant does not inherit that column from any other parents and never had an independent definition of the column. A nonrecursive DROP COLUMN (i.e., ALTER TABLE ONLY.

DROP COLUMN) never removes any descendant columns, but instead marks them as independently defined rather than inherited.The TRIGGER, CLUSTER, OWNER, and TABLESPACE actions never recurse to descendant tables; that is, they always act as though ONLY were specified. Adding a constraint recurses only for CHECK constraints that are not marked NO INHERIT.Changing any part of a system catalog table is not permitted.Refer to for a further description of valid parameters.

Has further information on inheritance.

PostgreSQL SERIAL data type does not provide options to set the start value and increment, but you can modify the sequence object assigned to SERIAL using ALTER SEQUENCE statement:CREATE TABLE teams2(id SERIAL UNIQUE,name VARCHAR (90 ) );- Modify initial value and increment ALTER SEQUENCE teams2idseq RESTART WITH 3 INCREMENT BY 3;- Insert data INSERT INTO teams2 (name ) VALUES ( 'Crystal Palace' );INSERT INTO teams2 (name ) VALUES ( 'Leeds United' );Table content:idname3Crystal Palace6Leeds United. There are several options to obtain the inserted ID value.

You can use LASTVAL function that returns the latest value for any sequence:INSERT INTO teams (name ) VALUES ( 'Manchester United' );SELECT LASTVAL ( );- Returns: 4You can also obtain the current value from the sequence object directly using CURRVAL function. The sequence name is tablenameserialcolseq:INSERT INTO teams (name ) VALUES ( 'Chelsea' );SELECT CURRVAL ( 'teamsidseq' );- Returns: 5Or you can use the RETURNING clause of INSERT statement to return ID:INSERT INTO teams (name ) VALUES ( 'Arsenal' ) RETURNING id;- Returns: 6How to Access Generated ID in ApplicationSELECT LASTVAL and SELECT CURRVAL return the generated ID as a single-row result set. In a.NET, Java or PHP application you can use appropriate methods to execute a query and read a row:. If you insert an ID value explicitly, it has no effect on the sequence generator, and its next value remains unchanged and will be used when you insert subsequent rows:- Insert ID 8 explicitly INSERT INTO teams VALUES ( 8, 'Everton' );- Continue using ID generator INSERT INTO teams (name ) VALUES ( 'Liverpool' ); - ID 7 is assignedNote that the sequence generator may have conflicts with IDs that were already inserted using explicit values.

You can get an error if there is an UNIQUE constraint, or duplicate IDs can be inserted:- Will try to assign ID 8 that already inserted INSERT INTO teams (name ) VALUES ( 'Some team' );- ERROR: duplicate key value violates unique constraint 'teamsidkey' - DETAIL: Key (id)=(8) already exists. Continue, now it will use ID 9 INSERT INTO teams (name ) VALUES ( 'Newcastle United' );Table content:idname1Tottenham Hotspur2Aston Villa3Manchester City0Reserved4Manchester United5Chelsea6Arsenal8Everton7Liverpool9Newcastle UnitedIf you remove rows from a table, you can insert removed IDs explicitly, it will not have any effect on the sequence generator. Converting PostgreSQL SERIAL columns:Oracle:Oracle does not support SERIAL (auto-increment, identity) columns, but this functionality can be implemented using a sequence and a trigger:CREATE TABLE teams(id NUMBER (10,0 ) UNIQUE,name VARCHAR2 (90 ) );CREATE SEQUENCE teamsidseq START WITH 1 INCREMENT BY 1;CREATE OR REPLACE TRIGGER teamsseqtrBEFORE INSERT ON teams FOR EACH ROWWHEN (NEW.id IS NULL ) BEGIN SELECT teamsidseq.