1. An SQL relation is defined by.

create table r (A1,D1,A2,D2, . . .,An,Dn
(integrity-constraint1),
. . . , (integrity-constraint1),

where r is the relation name, Ai is the name of an attribute, and Di is the domain of that attribute. The
allowed integrity-constraints include

primary key (Aj1, . . .,Ajm)

and
check(P)

2. Example.

create table branch (
bname char(15) not null
bcity char(30)
assets integer
primary key (bname)
check (assets >= 0))

3. The values of primary key must be not null and unique. SQL-92 consider not null in primary key speci cation
is redundant but SQL-89 requires to de ne it explicitly.

4. Check creates type checking functionality which could be quite useful. E.g.,

create table student (
name char(15) not null
student-id char(10) not null
degree-level char(15) not null
check (degree-level in ("Bachelors", "Masters", "Doctorate")))

5. Some checking (such as foreign-key constraints) could be costly, e.g.,
check (bname in (select bname from branch))

6. A newly loaded table is empty. The insert command can be used to load it, or use special bulk loader
untilities.

7. To remove a relation from the database, we can use the drop table command.

drop table r

This is not the same as

delete r

which retains the relation, but deletes all tuples in it.

8. The alter table command can be used to add or drop attributes to an existing relation r.

alter table r add A D

where A is the attribute and D is the domain to be added.

alter table r drop A

where A is the attribute to be dropped.