Consider a relational database containing the following schemas. The primary key of each table is indicated by underlining the constituent fields.SELECT s.sno, s.sname FROM Suppliers s, Catalogue c WHERE s.sno = c.sno AND cost > (SELECT AVG (cost) FROM Catalogue WHERE pno = 'P4' GROUP BY pno);The number of rows returned by the above SQL query is

To find the number of rows returned by the SQL query, we evaluate it step-by-step:

1. Subquery Evaluation: ```sql SELECT AVG (cost) FROM Catalogue WHERE pno = 'P4'GROUP BY pno;``` From the Catalogue table, the tuples with $\text{pno} = \text{'P4'}$ are:

   • $(\text{S2}, \text{P4}, 200)$

   • $(\text{S3}, \text{P4}, 250)$

   The average cost is:

   $$\text{AVG(cost)} = \frac{200 + 250}{2} = 225$$

2. Outer Query Condition: ```sql WHERE s.sno = c.sno AND cost > 225 ``` We find all rows in Catalogue where $\text{cost} > 225$:

   • Row 5: $(\text{S2}, \text{P5}, 250)$

   • Row 6: $(\text{S3}, \text{P1}, 250)$

   • Row 8: $(\text{S3}, \text{P5}, 300)$

   • Row 9: $(\text{S3}, \text{P4}, 250)$

3. Join and Projection: Joining these 4 rows with the Suppliers table on $\text{s.sno} = \text{c.sno}$ gives:

   • $(\text{S2}, \text{M/s Balaji furniture})$

   • $(\text{S3}, \text{M/s Premium furniture})$

   • $(\text{S3}, \text{M/s Premium furniture})$

   • $(\text{S3}, \text{M/s Premium furniture})$

   Since DISTINCT is not specified, all $4$ rows are returned.

Therefore, the number of rows returned is 4 (Option A).