#Postgresql cast null to timestamp for free#

If the cast is marked AS IMPLICIT then it can be invoked implicitly in any context, whether assignment or internally in an expression. (We generally use the term assignment cast to describe this kind of cast.)

Will be allowed if the cast from type integer to type text is marked AS ASSIGNMENT, otherwise not. For example, supposing that foo.f1 is a column of type text, then: If the cast is marked AS ASSIGNMENT then it can be invoked implicitly when assigning a value to a column of the target data type. An I/O conversion cast acts the same as a regular function-based cast only the implementation is different.īy default, a cast can be invoked only by an explicit cast request, that is an explicit CAST( x AS typename) or x :: typename construct. In many common cases, this feature avoids the need to write a separate cast function for conversion. An I/O conversion cast is performed by invoking the output function of the source data type, and passing the resulting string to the input function of the target data type. You can define a cast as an I/O conversion cast by using the WITH INOUT syntax. (Two types that are binary coercible both ways are also referred to as binary compatible.)

#Postgresql cast null to timestamp for free#

For example, the cast from xml to text can be performed for free in the present implementation, but the reverse direction requires a function that performs at least a syntax check. Binary coercibility is not necessarily a symmetric relationship. For instance, the types text and varchar are binary coercible both ways.

This requires that corresponding values use the same internal representation. Two types can be binary coercible, which means that the conversion can be performed “ for free” without invoking any function. (If no suitable cast has been defined, the conversion fails.) For example,Ĭonverts the integer constant 42 to type float8 by invoking a previously specified function, in this case float8(int4). A cast specifies how to perform a conversion between two data types.