type FuncFactory interface {
Function(name string) (api.Function, error)
// HasFunctionSet Some functions are bundled together into a plugin which shares the same json file.// This function can return if the function set name exists.
HasFunctionSet(funcName string) bool// ConvName Convert the name of the function usually to lowercase.// This is only be used when parsing the SQL statement.
ConvName(funcName string) (string, bool)
}