Consider a database that has the relation schema CR(StudentName, CourseName). An instance of the schema CR is as given below. The following query is made on the database. $$T1 \leftarrow \pi_{\text{CourseName}} (\sigma_{\text{StudentName} = '\text{SA}'}(\text{CR}))$$ $$T2 \leftarrow \text{CR} \div T1$$ The number of rows in $T2$ is _______.

First, evaluate intermediate relation $T1$:

From the given table, for StudentName = 'SA', the courses are:

Next, evaluate the relational division $T2 = \text{CR} \div T1$: The division operator $\text{CR} \div T1$ selects all distinct StudentName values that are associated with *all* courses present in $T1$ (i.e., CA, CB, and CC).

Let us check the courses taken by each student:

• SA: {CA, CB, CC} $\rightarrow$ contains all three courses.

• SB: {CB, CC} $\rightarrow$ does not contain CA.

• SC: {CA, CB, CC} $\rightarrow$ contains all three courses.

• SD: {CA, CB, CC, CD} $\rightarrow$ contains all three courses.

• SE: {CD, CA, CB} $\rightarrow$ does not contain CC.

• SF: {CA, CB, CC} $\rightarrow$ contains all three courses.

Thus, the students present in $T2$ are SA, SC, SD, and SF.

Therefore, the number of rows in $T2$ is 4 [cite: 2].