there are three class1,class2,class3 tables that represent three different classes. The structure of the table is the same, with two fields, name and birthday, indicating the student"s name and date of birth, respectively.
class1 data:
name birthday
james 1999-12-12
emma 1999-10-29
tom 2000-01-12
paul 1999-09-30
class2 data:
name birthday
tom 1997-01-09
john 1996-12-10
mike 1997-03-12
larry 1996-08-10
class3 data:
name birthday
peter 1998-03-12
tom 1998-08-31
milly 1997-05-12
benjamin 1997-12-12
so how to find names that exist in three class at the same time. (here is tom. )