QBE-Language a and Example S# NAME AGE SEX P.X <22 M 2、 SC S# C# GRADE P._SX C1 SX C2 (同时学习C1和C2) 3、SG S# C# GRADE SX P.PX ≠SX PX 147147 二、QBE-Language and Example 1、S S# NAME AGE SEX P.X <22 M 2、SC S# C# GRADE P. SX C1 SX C2 (同时学习C1和C2) 3、SC S# C# GRADE SX P. PX ≠SX PX