Question

关系代数 现有表test内有属性（t1,t2,t3）SQL语句：select *from test as A,test

Answer 1

2种解决办法

1.select *

from test

where t1 in (select t3 from test)

2.select *

from test a

where exists (select * from test b where a.t1=b.t3)

貌似不用连接,好像就这个意思select * from test where t1=t3

写成关系代数是

π testt1,t2,t3(б testt1=б testt2)

符号不好打