A table in a relational database is much like a table on paper: It consists of rows and columns. The number and order of the columns is fixed, and each column has a name. The number of rows is variable — it reflects how much data is stored at a given moment. SQL does not make any guarantees about the order of the rows in a table. When a table is read, the rows will appear in an unspecified order, unless sorting is explicitly requested. This is covered in Chapter 7. Furthermore, SQL does not ass

A composite type represents the structure of a row or record; it is essentially just a list of field names and their data types. PostgreSQL allows composite types to be used in many of the same ways that simple types can be used. For example, a column of a table can be declared to be of a composite type. 8.16.1. Declaration of Composite Types Here are two simple examples of defining composite types: CREATE TYPE complex AS ( r double precision, i double precision ); CREATE

NameCLUSTER -- cluster a table according to an index Synopsis CLUSTER [VERBOSE] table_name [ USING index_name ] CLUSTER [VERBOSE] Description CLUSTER instructs PostgreSQL to cluster the table specified by table_name based on the index specified by index_name. The index must already have been defined on table_name. When a table is clustered, it is physically reordered based on the index information. Clustering is a one-time operation: when the table is subsequently updated, the changes

This is a list of acronyms commonly used in the PostgreSQL documentation and in discussions about PostgreSQL. ANSI American National Standards Institute API Application Programming Interface ASCII American Standard Code for Information Interchange BKI Backend Interface CA Certificate Authority CIDR Classless Inter-Domain Routing CPAN Comprehensive Perl Archive Network CRL Certificate Revocation List CSV Comma Separated Values CTE Common Table Expression CVE Common Vulnerab

The functions and function-like expressions described in this section operate on values of type xml. Check Section 8.13 for information about the xml type. The function-like expressions xmlparse and xmlserialize for converting to and from type xml are not repeated here. Use of most of these functions requires the installation to have been built with configure --with-libxml. 9.14.1. Producing XML Content A set of functions and function-like expressions are available for producing XML content fr

When you create complex database structures involving many tables with foreign key constraints, views, triggers, functions, etc. you implicitly create a net of dependencies between the objects. For instance, a table with a foreign key constraint depends on the table it references. To ensure the integrity of the entire database structure, PostgreSQL makes sure that you cannot drop objects that other objects still depend on. For example, attempting to drop the products table we considered in Sect

PostgreSQL provides facilities to support dynamic tracing of the database server. This allows an external utility to be called at specific points in the code and thereby trace execution. A number of probes or trace points are already inserted into the source code. These probes are intended to be used by database developers and administrators. By default the probes are not compiled into PostgreSQL; the user needs to explicitly tell the configure script to make the probes available. Currently, th

Geometric data types represent two-dimensional spatial objects. Table 8-20 shows the geometric types available in PostgreSQL. Table 8-20. Geometric Types Name Storage Size Description Representation point 16 bytes Point on a plane (x,y) line 32 bytes Infinite line {A,B,C} lseg 32 bytes Finite line segment ((x1,y1),(x2,y2)) box 32 bytes Rectangular box ((x1,y1),(x2,y2)) path 16+16n bytes Closed path (similar to polygon) ((x1,y1),...) path 16+16n bytes Open path [(x1,y1),...] polygon 40+16n byt

The following "parameters" are read-only, and are determined when PostgreSQL is compiled or when it is installed. As such, they have been excluded from the sample postgresql.conf file. These options report various aspects of PostgreSQL behavior that might be of interest to certain applications, particularly administrative front-ends. block_size (integer) Reports the size of a disk block. It is determined by the value of BLCKSZ when building the server. The default value is 8192 bytes. The me

The catalog pg_trigger stores triggers on tables and views. See CREATE TRIGGER for more information. Table 50-49. pg_trigger Columns Name Type References Description oid oid Row identifier (hidden attribute; must be explicitly selected) tgrelid oid pg_class.oid The table this trigger is on tgname name Trigger name (must be unique among triggers of same table) tgfoid oid pg_proc.oid The function to be called tgtype int2 Bit mask identifying trigger firing conditions tgenabled char Cont