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One-to-one relationship:
For every 1:1 relationship type R in the ER diagram including two entities E1 and E2 we take one of entities (say E1) preferably with total participation and add primary key attribute of one more entity E2 as a foreign key attribute in the table of entity (E1). We will also have all the simple attributes of relationship type R in E1 if any.
For instance, the DEPARTMENT relationship has been extended to contain head-Id and attribute of the relationship. Please note we will maintain information in this table of only present head and Date from which s/he is the head.
There is one Head_of 1:1 relationship among FACULTY and DEPARTMENT. We select DEPARTMENT entity having total participation and add primary key attribute ID of FACULTY entity as a foreign key in DEPARTMENT entity named as Head_ID. Now the DEPARTMENT table will be as follows:
DEPARTMENT
D_NO
D_NAME
Head_ID
Date-from
What is the use of sub queries? A sub query is a select-from-where expression that is nested with in another query. A common use of sub queries is to do tests for set membershi
Sequences Sequences: Automatically produce unique numbers Are sharable Are typically used to make a primary key value Replace application code Speed up t
What are the parts of SQL language? The SQL language has various parts: data - definitition language Data manipulation language View definition Transaction contr
In the ER diagram, one example of subclassing is depicted following the Services entity. The subclasses Item Based and Time Based are created. The entity Services gains the attribu
In an E-R diagram an entity set is represent by? In an E-R digram entity set is represted by rectangle.
These are the binary operations; i.e., each is applied to two relations or sets. These two relations can be union compatible excluding in case of Cartesian product. Two relations R
differences between a classified catalog and a dictionary catalog
Implementation of association as an object Implement as a separate association object, independent of either class, as in Figure. An association object is a group of pairs
It can be easily defined as: The database must not have any unmatched foreign key values. The term "unmatched foreign key value" means a foreign key value for which there doe
WHAT IS SQL
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