A. GROUP BY B. ORDER BY C. FROM D. WHERE
A. ORDER BY B. WHERE C. GROUP BY D. FROM
A. 内连接 B. 外连接 C. 交叉连接 D. 自连接
A. 并 B. 交 C. 差 D. 笛卡尔积
A. CROSS JOIN B. INNER JOIN C. LEFT JOIN D. FULL JOIN