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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.
Compare the two log-based recovery schemes in terms of ease of implementation and overhead cost. Ans: There are two types of log based recovery techniques: deferred update
sir, could anybody help me in getting complete information about the mentioned topic
why shadow copy technique is used?
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What is NULL? Simply NULL means not in value.
What sorts of tables one can se in designing the hierarchy of a LDB? Tables, which are having Foreign Key relations.
System level permissions : With the use of data dictionary you can view them. Let us take the table name as user_sys_privs (used in oracle). DESCRIBE USER_SYS_PRI
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Consider the following database containing five transactions. Let min_sup = 60%. Mine all frequent itemsets using Apriori and FP-growth algorithm. Compare the efficiency of the t
Differentiate between Primary and secondary storage? Primary and secondary storage - Primary storage device stores the data temporarily. Primary storage is commonly used thro
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