数据库not exists真假判断

Question

这个第三小问可以写成SELECT ANAME,CITY FROM A,B,AB where A#=‘256’ and A.A# = AB.A# and B.B#=AB.B# 这种形式吗？？
还有使用not exists这样子对不SELECT ANAME,CITY FROM A WHERE NOT EXISTS(SELECT * FROM AB X WHERE X.A#='256' AND NOT EXISTS (SELECT * FROM AB Y WHERE A.A#=Y.A# AND Y.B#=X.B#));

Answer 1

商店代号、商品号是主键吗