Choose three.ide
Which three statements are true about defining relations between tables in a relatonal database?three
A) Foreign key columns allow null values.it
B) Unique key columns allow null valuesio
C) Primary key columns allow null values.table
D) Every primary or unique key value must refer to a matching foreign key value.class
E) Every foreign key value must refer to a matching primary or unique key value.im
Answer:ABEtab
(解析:AB Answer:比較簡單明瞭;D Answer:說反了)di