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Determine the Strong and Weak Entity
Based on the method of foreign key, there might be arise a situation when we have to relate an entity having a primary key of its own and an entity not having a primary key of its own. In such a case, the entity having its own primary key is known as a strong entity and the entity not having its own primary key is known as a weak entity. Whenever we need to relate a strong and a weak entity together, the ERD would alter just a little.
Say, for instance, we have a statement "A Student lives in a Home." STUDENT is obviously a strong entity having a primary key Roll. But HOME might not have a unique primary key, as its only attribute Address may be shared by a lot of homes (what if it is a housing estate?). HOME is a weak entity in this case.
In case of entity integrity, the primary key may be declared? In a case of entity integrity primary key may be not Null.
Define NULL value NULL value NULL means something is unknown. It does NOT mean null (the digit 0). Null is as well employed as attribute value for a particular entity in which
In E-R Diagram how relationship type is represented ? In E-R Diagram relationship type is represented as a Diamond.
WHY SHOULD NULL IN A RELATION BE AVOID AS possible?
What is the difference between WHERE and HAVING clauses?. Predicates in the WHERE clause applies to every tuple while the predicate in the HAVING clause applies to groups.
Multiple column Queries: Syntax: SELECT COLUMN1, COL2,...... FROM TABLE WHERE (COLUMN1, COL2, ...) IN (SELECT COLUMN1, COL2,.... FROM TABLE WHERE );
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);
The Update Operations : Update operations are used for altering database values. The constraint violations faced by this operation are logically the similar as the problem faced
What is a Built-in A notation of identity is built-into the data model or programming language and no user-supplied identifier is needed. This form of identity is used in objec
Difference between LEFT OUTER JOIN and RIGHT OUTER JOIN In left outer join tuples from the left-hand-side relation which do not match any tuple in the right-hand-side relation
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