If no argument list is specified, the function name must be unique in its schema. The function's result data type must match the target type of the cast. If it is not, the function will be looked up in the schema search path. The function name can be schema-qualified. The name of the target data type of the cast. The name of the source data type of the cast.
Cross-type-category casts, such as text to int4, are best made explicit-only. For example, the cast from int2 to int4 can reasonably be implicit, but the cast from float8 to int4 should probably be assignment-only. A good rule of thumb is to make a cast implicitly invokable only for information-preserving transformations between types in the same general type category. An overabundance of implicit casting paths can cause PostgreSQL to choose surprising interpretations of commands, or to be unable to resolve commands at all because there are multiple possible interpretations. It is wise to be conservative about marking casts as implicit. The fact that only one of the two casts is implicit is the way in which we teach the parser to prefer resolution of a mixed numeric-and- integer expression as numeric there is no built-in knowledge about that. Lacking any knowledge of which choice to prefer, it would give up and declare the query ambiguous. If that cast were marked AS IMPLICIT - which it is not - then the parser would be faced with choosing between the above interpretation and the alternative of casting the numeric constant to integer and applying the integer + integer operator. Now, the catalogs also provide a cast from numeric to integer. The parser will apply the implicit cast and resolve the query as if it had been written The query will therefore succeed if a cast from integer to numeric is available and is marked AS IMPLICIT - which in fact it is. There is no integer + numeric operator in the system catalogs, but there is a numeric + numeric operator. The parser initially marks the constants as being of type integer and numeric respectively.
(We generally use the term implicit cast to describe this kind of cast.) For example, consider this query: 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 DECIMAL TO INTEGER 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).
POSTGRESQL CAST DECIMAL TO INTEGER HOW TO
A cast specifies how to perform a conversion between two data types.
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