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It defines that no primary key value can be null. This is as the primary key is used to recognize individual tuple in the relation. So we will not be able to recognize the records uniquely containing null values for the primary key attributes. This constraint is specified on single individual relation.
Example: Let R be the Table
A#
B
C
Null
B1
C1
A2
B2
C2
B3
C3
A4
B4
A5
C5
Note:
1) '#' shows the Primary key of a relation.
In the relation R above, the primary key has null values in the tuples t1 & t3. NULL value in primary key is not allowed, therefore, relation instance is an invalid instance.
1. Create a subroutine that does the remote blast on the file protein.fa. 2. Pass that returned files from the blast to another subroutine that parses the output and sends it to
CREATE TABLE prodtrans ( pno number (4) ptype char (1) CHECK (ptype in ('I','R','S')), qty number (5) FOREIGN KEY pno REFERENCES product (pno) ON DELETE CASCADE);
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1. Staff(staffID, firstName, lastName, availabilityID, experience, phone, mobile, email); 2. Availability(availabilityID, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday,
explain the level architectures of the database management system
why we fregment at all?
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Write the motivations led to development of OO-DBMS? 1. Programmer frustration with RDBMSs. 2. Requirement for special features.
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