PostgreSQL Alter Table Add Primary Key

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To be able to create a table, you must have USAGE privilege on all column types or the type in the OF clause, respectively. This parameter cannot be set for TOAST tables. 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.

PostgreSQL: Primary Keys This PostgreSQL tutorial explains how to create, drop, disable, and enable a primary key in PostgreSQL with syntax and examples. Referential actions other than the NO ACTION check cannot be deferred, even if the constraint is declared deferrable.

How to Create a Table in PostgreSQL

The table will be owned by the user issuing the command. If a schema name is given for example, CREATE TABLE myschema. Otherwise it is created in the current schema. Temporary tables exist in a special schema, so a schema name cannot be given when creating a temporary table. The name of the table 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. The optional constraint clauses specify constraints 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 for use when 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. The cannot access and therefore cannot vacuum or analyze temporary tables. For this reason, appropriate vacuum and analyze operations should be performed via session SQL commands. For example, if a temporary table is going to be used in complex queries, it is wise to run ANALYZE on the temporary table after it is populated. Optionally, GLOBAL or LOCAL can be written before TEMPORARY or TEMP. This makes no difference in PostgreSQL, but see. A typed table is tied to its type; for example the table will be dropped if the type is dropped with DROP TYPE... 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. This can include array specifiers. For more information on the data types supported by PostgreSQL, refer to. 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. 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. Constraints having the same name and expression will be merged into one copy. 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. 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 only be copied 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. Not-null constraints are always copied to the new table. CHECK constraints will only be copied if INCLUDING CONSTRAINTS is specified; other types of constraints will never be copied. Also, no distinction is made between column constraints and table constraints — when constraints are requested, all check constraints are copied. Any indexes on the original table will not be created on the new table, unless the INCLUDING INDEXES clause is specified. STORAGE settings for the copied column definitions will only be copied 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 STORAGE settings, see. Comments for the copied columns, constraints, and indexes will only be copied 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 CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS. Note also 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 signalled. 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 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 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. 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 can 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. 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. The operators are required to be commutative. The access method must support amgettuple see ; 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. 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. If refcolumn 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. 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 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. Referential actions other than the NO ACTION check 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 value of the referencing column to the new value of the referenced column, respectively. SET NULL Set the referencing column s to null. SET DEFAULT Set the referencing column s to their default values. If the referenced column s are changed frequently, it might be wise to add an index to the foreign key column so that referential actions associated with the foreign key column 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 command. 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. 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. If OIDS is not specified, the default setting depends upon the configuration parameter. 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. If you wish to give both an OIDS setting and storage parameters, you must use the WITH... 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. TABLESPACE tablespace The tablespace is the name of the tablespace in which the new table is to be created. If not specified, is consulted, or if the table is temporary. USING INDEX TABLESPACE tablespace This clause allows selection of the tablespace in which the index associated with a UNIQUE, PRIMARY KEY, or EXCLUDE constraint will be created. If not specified, is consulted, or if the table is temporary. 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. The storage parameters currently available for tables are listed below. For each parameter, unless noted, there is an additional parameter with the same name prefixed with toast. 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. If false, this table will not be autovacuumed, except to prevent transaction Id wraparound. See for more about wraparound prevention. Observe that this variable inherits its value from the setting. Notes 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 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. 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 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. 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. 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. Be aware that this can be significantly slower than immediate uniqueness checking. 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. Typed Tables Typed tables implement a subset of the SQL standard. PostgreSQL does not support these self-referencing columns explicitly, but the same effect can be had using the OID feature.

First we need to create the extension in the database we wish to use it with, CREATE EXTENSION pgcrypto; This is how you load pre-compiled shared library code which adds functionality into your PostgreSQL database. The LIKE clause can also be used to copy column definitions from views, foreign tables, or composite types. Typically, when initially setting up a hash-partitioned table, you should choose a modulus equal to the number of partitions and assign every table the same modulus and a different remainder see examples, below. Currently, postgresql create table primary key works reliably for functions on the first or only parent table, but not so well for functions on additional parents. I cannot understand the syntax error in creating a composite key. Refer to the PostgreSQL User's Guide for further information about data types and arrays. 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. It is therefore crucial that you do your utmost to add that all-important primary key column to every table, and thankfully Postgres provides two methods for accomplishing this task. Typed Tables Typed tables implement a subset of the SQL standard. 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. 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. Referential actions other than the Postgresql create table primary key ACTION check cannot be deferred, even if the constraint is declared deferrable.