NewDDLExecutor creates DDL executor.

NewDeleteExecutor creates new delete executor.

NewInsertExecutor creates new insert executor.

NewOthersExecutor -- creates new others executor.

NewSelectExecutor creates the new select executor.

NewTree creates the new execute tree.

NewUnionExecutor creates the new select executor.

NewUpdateExecutor creates the new update executor.

DDLExecutor represents a CREATE, ALTER, DROP executor.

DeleteExecutor represents delete executor.

InsertExecutor represents insert executor.

OthersExecutor -- represents special executor.

SelectExecutor represents select executor.

Tree is a container for all executors.

UnionExecutor represents select executor.

UpdateExecutor represents update executor.

Executor interface.