@PublicEvolving public abstract class UserDefinedFunction extends Object implements FunctionDefinition, Serializable
User-defined functions combine the logical definition of a function for validation and
FunctionDefinition) and contain a corresponding runtime implementation.
A runtime implementation might be called at two different stages:
FunctionDefinition.isDeterministic()to disable constant expression reduction in this case. For example, the following calls to
ABSare executed during planning:
SELECT ABS(-1) FROM tand
SELECT ABS(field) FROM t WHERE field = -1.
|Constructor and Description|
|Modifier and Type||Method and Description|
Tear-down method for user-defined function.
Returns a unique, serialized representation for this function.
Returns the logic for performing type inference of a call to this function definition.
Setup method for user-defined function.
Returns the name of the UDF that is used for plan explanation and logging.
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
getKind, getRequirements, isDeterministic
public final String functionIdentifier()
public void open(FunctionContext context) throws Exception
public void close() throws Exception
public abstract TypeInference getTypeInference(DataTypeFactory typeFactory)
The type inference process is responsible for inferring unknown types of input arguments, validating input arguments, and producing result types. The type inference process happens independent of a function body. The output of the type inference is used to search for a corresponding runtime implementation.
Instances of type inference can be created by using
BuiltInFunctionDefinitions for concrete usage examples.
The type inference for user-defined functions is automatically extracted using reflection.
It does this by analyzing implementation methods such as
eval() or accumulate() and
the generic parameters of a function class if present. If the reflective information is not
sufficient, it can be supported and enriched with
Note: Overriding this method is only recommended for advanced users. If a custom type inference is specified, it is the responsibility of the implementer to make sure that the output of the type inference process matches with the implementation method:
The implementation method must comply with each
returned by the type inference. For example, if
DataTypes.TIMESTAMP(3).bridgedTo(java.sql.Timestamp.class) is an expected argument type, the
method must accept a call
Regular Java calling semantics (including type widening and autoboxing) are applied when
calling an implementation method which means that the signature can be
The runtime will take care of converting the data to the data format specified by the
DataType.getConversionClass() coming from the type inference logic.
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