Grouping statement enum by macro-categories

At this time, the statements enum is massive and includes all SQL statements. What if we were to create sub-enum categories, such as DML, DDL DQL, DCL, TCL, SCL, PSM and so on?

This would clearly break APIs, but it would make much more manageable to work with statements, expecially in the cases where only a subset of the statements are desidered.

Luca

首先定位 statements enum，並審查其公開 API 及其使用情況。定義提議的 SQL 宏類別，並評估 API 破壞和相容性影響；當類別結構和受影響的介面達成共識，並由相關 parser 測試涵蓋時，工作即告完成。

由索引模型根據 Issue 內容生成。