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What is a foreign key, and what is it used for?
A foreign key is used to establish relationships between relations in the relational model. Technically, a foreign key is a column (or columns) appearing in one relation that is (are) the primary key of another table. Although there might be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence necessity is created in a database using a referential integrity constraint on the foreign key.
Concurrency issues Data integrity: Threads accessing same object need to be synchronized, such as: banking account. Deadlock: One or more threads in system are perman
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);
What is the difference among a database schema and a database state? The collection of information stored in database at particular moment in time is known as database state a
Define the terms 1) physical schema 2) logical schema. Physical schema: The physical schema explains the database design at the physical level, which is the lowest lev
Although how will the system recover The selection of REDO or UNDO for a transaction for the recovery is completed on the basis of the state of the transactions. This state is
Scenario: You are a freelance database designer who has just been contacted by a small software development company named Altair Software. The president of the company has asked
Equi Join: A join in which the joining condition is based on equality among values in the common columns. Common columns show (redundantly) in the result table. Let us Consider th
coventions for displaying an ER schema as ER diagram
Consider the two relations given below Given that A is the primary key of R, D is the primary key of S and there is a referential integrity among S.A and R.A, discuss all
Rearrange Classes and Operations Sometimes, the similar operation is defined across different classes and can easily be inherited from a familiar ancestor, but more often oper
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