|The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 454 pages
RRP £14.95 ($19.95)
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184.108.40.206 Constants of Other Types
A constant of an arbitrary type can be entered using any one of the following notations:
type 'string' 'string'::type CAST ( 'string' AS type )
The string constant's text is passed to the input conversion routine for the type called type. The result is a constant of the indicated type. The explicit type cast can be omitted if there is no ambiguity as to the type the constant must be (for example, when it is assigned directly to a table column), in which case it is automatically coerced.
The string constant can be written using either regular SQL notation or dollar-quoting.
It is also possible to specify a type coercion using a function-like syntax:
typename ( 'string' )
but not all type names can be used in this way; see section 2.2.9 Type Casts for details.
function-call syntaxes can also be used to specify run-time type
conversions of arbitrary expressions, as discussed in section 2.2.9 Type Casts. To avoid syntactic ambiguity, the
syntax can only be used to specify the type of a simple literal constant.
Another restriction on the
syntax is that it does not work for array types; use
CAST() to specify the type of an array constant.
CAST() syntax conforms to SQL. The
syntax is a generalization of the standard: SQL specifies this syntax only
for a few data types, but PostgreSQL allows it
for all types. The syntax with
:: is historical PostgreSQL
usage, as is the function-call syntax.
|ISBN 9781906966041||The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference||See the print edition|