Using the field-constraint-def clause you can name or specify the
type of field-level constraints to be defined within a specific
relation definition.
(B)0[mfield-constraint-def =
qwqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqk
mq> [4mCONSTRAINT[m constraint-name IS qqj x
lqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqj
mwq> [4mNOT[m [4mMISSING[m qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqk
tq> [4mUNIQUE[m qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu x
tq> [4mPRIMARY[m [4mKEY[m qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu x
mw> [4mREFERENCES[m referenced-relation-name qwqqqqqqqqqqqqqqqqqqqqqqqqwu x
x m> referenced-field-name jx x
x x x
mq> [4mUSING[m rse [4mREQUIRE[m conditional-expr qqqqqqqqqqqq>qqqqqqqqqqqqqqj x
x
lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
mwqqqqqqqqqqqqqqqqqqqqqqqqqqqwq>
mqq> [4mCHECK[m ON qwqq> [4mCOMMIT[m qu
mqq> [4mUPDATE[m qj
1 – constraint-name
The name of a field constraint associated with the relation that
is being defined. This name must be unique within the database.
The constraint name can be referred to in other statements such
as CHANGE RELATION, SHOW CONSTRAINT, and START_TRANSACTION.
The clause 'CONSTRAINT constraint-name IS' is optional. If you
do not specify the keyword CONSTRAINT, Oracle Rdb provides a name
for the constraint. However, Rdb recommends that you always
name field and relation constraints. The alternative is to have
constraints named by the database system with names such as
LAST_NAME_REQUIRE_0001.
2 – NOT_MISSING
Restricts field values such that none of the values for the
specified field can assume either the defined or default missing
value for that field. You can only explicitly declare the NOT
MISSING clause at the field level.
3 – UNIQUE
This clause names a field in the relation which is a part of
a unique key. This field name can appear only once in the key
definition.
The UNIQUE clause limits field values such that no two rows in
the associated relation can have the same non-missing values for
the specified field or fields.
4 – PRIMARY
This clause names a field in the relation which is a part of a
primary key. This field name can appear only once in the base
relation. Oracle Rdb requires that the values in a primary key
be unique and not missing; therefore, you need not specify the
UNIQUE and NOT MISSING field constraints for a field that you
designate a primary key. Only one primary key can be declared for
a relation.
5 – referenced-relation-name
The name of the relation that defines the unique or primary
key definition which is referred to by a foreign key of this
relation. If there are no referenced-field-names specified with
this relation-name, then the referenced-relation must have an
associated constraint which specifies a primary key. If there
are referenced-field-names, the referenced-relation must have a
unique or primary key constraint defined which specifies a list
of unique-field-names. These names have to be the same names as
in the referenced-relation.
6 – referenced-field-name
Specifies the name of a field in the foreign key relation that
corresponds to the field with the same ordinal position within
the list of fields referred to by the primary key relation.
7 – rse
A record selection expression that defines which records of which
relations will be tested against the conditional expression. This
rse cannot refer to any host variables.
8 – conditional-expression
An expression that describes the optional conditions that must be
satisfied before the record can be stored in the database.
9 – CHECK
Declares the time when the constraint is evaluated. The
referential constraint can be evaluated when the update occurs
(CHECK ON UPDATE) or when a COMMIT is issued (CHECK ON COMMIT).
The EVALUATING clause of the START_TRANSACTION statement can
override the CHECK ON clause.