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Chapter 8. Data Types

Table of Contents
Numeric Types
Monetary Type
Character Types
Date/Time Types
Boolean Type
Geometric Types

Describes the built-in data types available in Postgres.

Postgres has a rich set of native data types available to users. Users may add new types to Postgres using the define type command described elsewhere.

In the context of data types, the following sections will discuss SQL standards compliance, porting issues, and usage. Some Postgres types correspond directly to SQL92-compatible types. In other cases, data types defined by SQL92 syntax are mapped directly into native Postgres types. Many of the built-in types have obvious external formats. However, several types are either unique to Postgres, such as open and closed paths, or have several possibilities for formats, such as date and time types.

Table 8-1. Postgres Data Types

Postgres

SQL92

SQL3

Description
bool boolean logical boolean (true/false)
box rectangular box in 2D plane
char(n) character(n) fixed-length character string
circle circle in 2D plane
date date calendar date without time of day
float4/8 float(p) floating-point number with precision p
float8 real, double precision double-precision floating-point number
int2 smallint signed two-byte integer
int4 int, integer signed 4-byte integer
int4 decimal(p,s) exact numeric for p <= 9, s = 0
int4 numeric(p,s) exact numeric for p == 9, s = 0
line infinite line in 2D plane
lseg line segment in 2D plane
money decimal(9,2) US-style currency
path open and closed geometric path in 2D plane
point geometric point in 2D plane
polygon closed geometric path in 2D plane
time time time of day
timespan interval general-use time span
timestamp timestamp with time zone date/time
varchar(n) character varying(n) variable-length character string

Table 8-2. Postgres Function Constants

Postgres

SQL92

Description
getpgusername() current_user user name in current session
date('now') current_date date of current transaction
time('now') current_time time of current transaction
timestamp('now') current_timestamp date and time of current transaction

Postgres has features at the forefront of ORDBMS development. In addition to SQL3 conformance, substantial portions of SQL92 are also supported. Although we strive for SQL92 compliance, there are some cases in the standard which are ill considered and which should not live through subsequent standards. Postgres will not make great efforts to conform to these cases. However, these cases tend to be little-used and obsure, and a typical user is not likely to run into them.

Although most of the input and output functions corresponding to the base types (e.g., integers and floating point numbers) do some error-checking, some are not particularly rigorous about it. More importantly, few of the operators and functions (e.g., addition and multiplication) perform any error-checking at all. Consequently, many of the numeric operators can (for example) silently underflow or overflow.

Some of the input and output functions are not invertible. That is, the result of an output function may lose precision when compared to the original input.


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