Entity integrity in DBMS, Define entity integrity, entity integrity examples
Entity
Integrity
Entity integrity and referential integrity are the
basic set of rules for the relational model. Entity integrity defines the properties
that are to be satisfied by a primary key.
We all know that a primary key is UNIQUE + NOT NULL. That
is, it cannot contain duplicate values and NULL values. This is what entity integrity
is all about.
Entity integrity - No component of a
primary key is allowed to have NULL values.
Example 1:
STUDENT (Register_Number, Name, Date_Of_Birth,
Phone)
In this table STUDENT, the attribute Register_Number is
the primary key. Hence, it cannot contain NULL value in it.
Example 2:
STUDENT_COURSE (Register_Number, Subject_Code,
Registered_Date)
Assume that the table given above is to store the subjects
that are registered by a student. A student may register one or more subjects. Hence,
the key for this table is a composite key which consists of (Register_Number,
Subject_Code).
In this case, neither Register_Number nor Subject_Code
can contain NULL values.
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