A database is a named collection of SQL objects ("database objects"). Generally, every database object (tables, functions, etc.) belongs to one and only one database. (However there are a few system catalogs, for example pg_database, that belong to a whole cluster and are accessible from each database within the cluster.) More accurately, a database is a collection of schemas and the schemas contain the tables, functions, etc. So the full hierarchy is: server, database, schema, table (or some o

PostgreSQL provides a rich set of tools for developers to manage concurrent access to data. Internally, data consistency is maintained by using a multiversion model (Multiversion Concurrency Control, MVCC). This means that each SQL statement sees a snapshot of data (a database version) as it was some time ago, regardless of the current state of the underlying data. This prevents statements from viewing inconsistent data produced by concurrent transactions performing updates on the same data row

Because roles can own database objects and can hold privileges to access other objects, dropping a role is often not just a matter of a quick DROP ROLE. Any objects owned by the role must first be dropped or reassigned to other owners; and any permissions granted to the role must be revoked. Ownership of objects can be transferred one at a time using ALTER commands, for example: ALTER TABLE bobs_table OWNER TO alice; Alternatively, the REASSIGN OWNED command can be used to reassign ownership

PostgreSQL provides a set of default roles which provide access to certain, commonly needed, privileged capabilities and information. Administrators can GRANT these roles to users and/or other roles in their environment, providing those users with access to the specified capabilities and information. The default roles are described in Table 21-1. Note that the specific permissions for each of the default roles may change in the future as additional capabilities are added. Administrators should

A column can be assigned a default value. When a new row is created and no values are specified for some of the columns, those columns will be filled with their respective default values. A data manipulation command can also request explicitly that a column be set to its default value, without having to know what that value is. (Details about data manipulation commands are in Chapter 6.) If no default value is declared explicitly, the default value is the null value. This usually makes sense be

61.4.1. GiST buffering build Building large GiST indexes by simply inserting all the tuples tends to be slow, because if the index tuples are scattered across the index and the index is large enough to not fit in cache, the insertions need to perform a lot of random I/O. Beginning in version 9.2, PostgreSQL supports a more efficient method to build GiST indexes based on buffering, which can dramatically reduce the number of random I/Os needed for non-ordered data sets. For well-ordered data se

Bit strings are strings of 1's and 0's. They can be used to store or visualize bit masks. There are two SQL bit types: bit(n) and bit varying(n), where n is a positive integer. bit type data must match the length n exactly; it is an error to attempt to store shorter or longer bit strings. bit varying data is of variable length up to the maximum length n; longer strings will be rejected. Writing bit without a length is equivalent to bit(1), while bit varying without a length specification means

NameDROP USER -- remove a database role Synopsis DROP USER [ IF EXISTS ] name [, ...] Description DROP USER is simply an alternate spelling of DROP ROLE. Compatibility The DROP USER statement is a PostgreSQL extension. The SQL standard leaves the definition of users to the implementation. See Also DROP ROLE Prev Next DROP TYPE Up DROP USER MAPPING

NameDROP VIEW -- remove a view Synopsis DROP VIEW [ IF EXISTS ] name [, ...] [ CASCADE | RESTRICT ] Description DROP VIEW drops an existing view. To execute this command you must be the owner of the view. Parameters IF EXISTS Do not throw an error if the view does not exist. A notice is issued in this case. name The name (optionally schema-qualified) of the view to remove. CASCADE Automatically drop objects that depend on the view (such as other views), and in turn all object

Before we proceed, you should understand the basic PostgreSQL system architecture. Understanding how the parts of PostgreSQL interact will make this chapter somewhat clearer. In database jargon, PostgreSQL uses a client/server model. A PostgreSQL session consists of the following cooperating processes (programs): A server process, which manages the database files, accepts connections to the database from client applications, and performs database actions on behalf of the clients. The database