Consider the following statement:S1: Deletion in referencing relation causes deletion anomaly.S2: Referential integrity constraints are specified between exactly two relations in a schema.S3: Count(*) also counts the tuples which consist of NULL in a relation.S4: Every relation is possible to decompose into BCNF with dependency preserving and lossless join decomposition.Which option is correct?a)S1, S2 are falseb)Only S3 is falsec)S2 and S3 are falsed)All Are FalseCorrect answer is option 'D'. Can you explain this answer?

Question

Answer

Analysis of Statements
To evaluate the correctness of the statements, let's consider each one closely:
Statement S1: Deletion in referencing relation causes deletion anomaly.
- This statement is true. Deletion anomalies occur when the deletion of a tuple in a relation leads to unintended loss of data in other related tuples. For example, if you delete a customer who has orders, you may inadvertently lose all information about their orders if it's not properly handled.
Statement S2: Referential integrity constraints are specified between exactly two relations in a schema.
- This statement is false. Referential integrity constraints can exist between more than two relations. A foreign key in one relation can reference a primary key in another, but it can also be part of a more complex relationship involving multiple tables.
Statement S3: Count(*) also counts the tuples which consist of NULL in a relation.
- This statement is false. The Count(*) function counts all the rows in a table, regardless of whether they contain NULL values. However, if we use Count(column_name), it will not count rows where that specific column is NULL.
Statement S4: Every relation is possible to decompose into BCNF with dependency preserving and lossless join decomposition.
- This statement is false. While every relation can be decomposed into BCNF, it is not always possible to do so while preserving all functional dependencies and ensuring a lossless join. Some decompositions may lose dependencies or may not be lossless.
Conclusion
- Since S2, S3, and S4 are false, and S1 is true, the correct answer is option 'D': All are false. However, S1 is actually true, indicating that the correct answer should be reconsidered based on the evaluation of S1.

Answer

S1: Referencing relation is the relation referring to a primary key of some other relation. Deletion in that table will not cause any violation. Hence, no deletion anomaly hence this is true.

So, this statement is true.

S2: This statement is true, since foreign key can be created within a relation

C is a foreign key referring to the primary key 'A'' of the same relation R.

S3: S3 is true since count (*) will count the no. of tuples in a relation, on the basis of ID value.

S4: It is true. Since it is possible to decompose every relation into BCNF with lossless join decomposition property but it may or may not preserve the dependencies of the relation.

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