1) Give an example of an attribute (or set of attributes) that you can deduce is

Question

1) Give an example of an attribute (or set of attributes) that you can deduce is not a candidate key, based on this instance being legal.

2) Is there any example of an attribute (or set of attributes) that you can deduce is a candidate key, based on this instance being legal?

3) Add another student in History 105 to the table and give student 53831 another course: show the resulting table

4) What is the only candidate key (and thus the primary key) of this table?

Foreign key Primary key grade, studid^sid login name Carnatic 101 C 53831 dave acs Reggae203B 53832., »53666 Jones onesacs 53688 Smith smithaee 50000 Dave 19 3.3 18 3.4 18 3.2 193.8 1.8 12 2.0 Topology 112 A 5365 History 105 B 5366653650 Smith smith@math 53831 Madayan madayan@music 3832 Guldu guldumusic Enrolled (Referencing relation) Students (Referenced relation) Figure 3.4 Referential Integrity

Explanation / Answer

1) Attributes which cannot be candidate key ----

grade ---- more than one students can have the same grade. So it is not unique.

name ---- more than one students can have the same name. So it is not unique.

age ---- more than one students can have the same age. So it is not unique.

2) Attributes which can be candidate keys

cid ---- course id is unique and not null

sid ---- student id is unique and not null

login ---- login is unique and not null

3

4. Primary keys

Student Table ---- sid

Course Table --- cid

Do ask if any doubt. Please upvote.

History105 B 53666 ---> 53831 Madayan madayan@music 11 1.8

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