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A relational database contains two tables Student and Performance as shown below:

$$\overset{\text{Table: student}}{\begin{array}{|l|l|} \hline \text{Roll_no} & \text{Student_name}\\\hline 1 & \text{Amit} \\\hline 2 & \text{Priya} \\\hline 3 & \text{Vinit} \\\hline 4 & \text{Rohan} \\\hline 5 & \text{Smita} \\\hline \end{array}} \qquad\overset{\text{Table: Performance}}{\begin{array}{|l|l|l|} \hline \text{Roll_no} & \text{Subject_code} & \text{Marks}\\\hline 1 & \text{A} & 86 \\\hline 1 & \text{B} & 95 \\\hline 1 & \text{C} & 90 \\\hline 2 & \text{A} & 89 \\\hline 2 & \text{C} & 92 \\\hline 3 & \text{C} & 80 \\\hline \end{array}}$$

The primary key of the Student table is Roll_no. For the performance table, the columns Roll_no. and Subject_code together form the primary key. Consider the SQL query given below:

SELECT S.Student_name, sum(P.Marks) FROM Student S, Performance P WHERE P.Marks >84 GROUP BY S.Student_name;

The number of rows returned by the above SQL query is ________

Reenakhanna That is on natural join, here cross product is considered as join condition is not given.

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35 votes

Best answer

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20 votes

6 votes

Remember this basic rule in sql

SELECT= PROJECTION

FROM= CROSS PRODUCT

WHERE= SELECT CONDITION

here in the given query we need to take cross product which returns 25 query with keeping in mind the condition to jave marks > 84 so when we group by our answer would be

Amit 452

Priya 452

Vinit 452

Roshan 452

Smita 452

So 5 tuples

SELECT= PROJECTION

FROM= CROSS PRODUCT

WHERE= SELECT CONDITION

here in the given query we need to take cross product which returns 25 query with keeping in mind the condition to jave marks > 84 so when we group by our answer would be

Amit 452

Priya 452

Vinit 452

Roshan 452

Smita 452

So 5 tuples

4 votes

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