FunctionLookup (Flink : Table : API Java 1.19.1 API)

```
@Internal
public interface FunctionLookup
```
Catalog of functions that can resolve the name of a function to a ContextResolvedFunction.

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`default ContextResolvedFunction`	`lookupBuiltInFunction(org.apache.flink.table.functions.BuiltInFunctionDefinition definition)` Helper method for looking up a built-in function.
`Optional<ContextResolvedFunction>`	`lookupFunction(String stringIdentifier)` Lookup a function by function identifier.
`Optional<ContextResolvedFunction>`	`lookupFunction(org.apache.flink.table.catalog.UnresolvedIdentifier identifier)` Lookup a function by function identifier.

lookupFunction
```
Optional<ContextResolvedFunction> lookupFunction(String stringIdentifier)
```
Lookup a function by function identifier. The identifier is parsed The lookup is case insensitive.

Optional<ContextResolvedFunction> lookupFunction(org.apache.flink.table.catalog.UnresolvedIdentifier identifier)

Lookup a function by function identifier. The lookup is case insensitive.

default ContextResolvedFunction lookupBuiltInFunction(org.apache.flink.table.functions.BuiltInFunctionDefinition definition)

Helper method for looking up a built-in function.

Interface FunctionLookup