1、IN 关键字
SECLET * FROM SCORES WHERE gno IN
（SECLET gno FROM games WHERE gtype=’棋牌‘）
注意：子查询一般不写成SECLET *FROM....
2、EXISTS关键字
SECLET * FROM SCORES
WHERE EXISTS
(SECLET * FROM USERS WHERE USER_NAME='孙悟空’)
1、IN 关键字
SECLET * FROM SCORES WHERE gno IN
（SECLET gno FROM games WHERE gtype=’棋牌‘）
注意：子查询一般不写成SECLET *FROM....
2、EXISTS关键字
SECLET * FROM SCORES
WHERE EXISTS
(SECLET * FROM USERS WHERE USER_NAME='孙悟空’)