单项选择题
A.安全性 B.完整性 C.移植性 D.一致性
A.SELECT S#,SNAME FROM S WHERE SNAME =′刘%′ B.SELECT S#,SNAME FROM S WHERE SNAME =′刘_′ C.SELECT S#,SNAME FROM S WHERE SNAME LIKE′刘%′ D.SELECT S#,SNAME FROM S WHERE SNAME LIKE′刘_′
A.R×S B.R∪S C.R∩S D.R-S