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• Students(stulD, lastName, firstName, major, credits) • Faculty (facID, name, deptName, rank) • Classes(classNumber, facID, schedule, room) • Enrolls(stulD, classNumber, grade) The primary keys are underlined. The referential integrity constraints are as follows: • the column facID of relation Classes that references table Faculty, . the column stulD of relation Enrolls that references table Students, and . the column classNumber of relation Enrolls that references table Classes The following query is intended to retrieve the number of all classes taught by John Smith in the CST department. However, this query does not work properly. There are at least two faculty members who share the name, John Smuth. Brefly explain why. and show the corrected SQL query_ SELECT classNumber FROM Classes WHERE facID- (SELECT facID FROM Faculty WHERE name -'John Smith' AND deptName -'CST');

• Students(stulD, lastName, firstName, major, credits) • Faculty (facID, name, deptName, rank) • Classes(classNumber, facID, schedule, room) • Enrolls(stulD, classNumber, grade) The primary keys are underlined. The referential integrity constraints are as follows: • the column facID of relation Classes that references table Faculty, . the column stulD of relation Enrolls that references table Students, and . the column classNumber of relation Enrolls that references table Classes The following query is intended to retrieve the number of all classes taught by John Smith in the CST department. However, this query does not work properly. There are at least two faculty members who share the name, John Smuth. Brefly explain why. and show the corrected SQL query_ SELECT classNumber FROM Classes WHERE facID- (SELECT facID FROM Faculty WHERE name -'John Smith' AND deptName -'CST');

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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### Database Schema and SQL Query Example #### Database Schema - **Students(stuID, lastName, firstName, major, credits)** - **Faculty(facID, name, deptName, rank)** - **Classes(classNumber, facID, schedule, room)** - **Enrolls(stuID, classNumber, grade)** Primary keys are underlined. The referential integrity constraints are as follows: - The column **facID** of relation **Classes** that references table **Faculty**. - The column **stuID** of relation **Enrolls** that references table **Students**. - The column **classNumber** of relation **Enrolls** that references table **Classes**. #### Problem Scenario The following SQL query is intended to retrieve the number of all classes taught by John Smith in the CST department. However, this query does not work properly because there are at least two faculty members who share the name "John Smith." Briefly explain why and show the corrected SQL query. #### Incorrect SQL Query ```sql SELECT classNumber FROM Classes WHERE facID = ( SELECT facID FROM Faculty WHERE name = 'John Smith' AND deptName = 'CST' ); ``` #### Explanation The issue with the above query is that the subquery can return more than one facID since there are multiple faculty members named "John Smith." This causes the main query to fail because it expects a single value for facID. #### Corrected SQL Query To fix this issue, we should use the `IN` operator instead of `=` to handle multiple values returned by the subquery: ```sql SELECT classNumber FROM Classes WHERE facID IN ( SELECT facID FROM Faculty WHERE name = 'John Smith' AND deptName = 'CST' ); ``` By using `IN`, we ensure that the query works correctly even if there are multiple faculty members named "John Smith." #### Conclusion In situations where subqueries might return multiple results, it's important to choose the appropriate operator to handle those results. Using `IN` instead of `=` can prevent errors when dealing with potential multiple matches.
Transcribed Image Text:### Database Schema and SQL Query Example #### Database Schema - **Students(stuID, lastName, firstName, major, credits)** - **Faculty(facID, name, deptName, rank)** - **Classes(classNumber, facID, schedule, room)** - **Enrolls(stuID, classNumber, grade)** Primary keys are underlined. The referential integrity constraints are as follows: - The column **facID** of relation **Classes** that references table **Faculty**. - The column **stuID** of relation **Enrolls** that references table **Students**. - The column **classNumber** of relation **Enrolls** that references table **Classes**. #### Problem Scenario The following SQL query is intended to retrieve the number of all classes taught by John Smith in the CST department. However, this query does not work properly because there are at least two faculty members who share the name "John Smith." Briefly explain why and show the corrected SQL query. #### Incorrect SQL Query ```sql SELECT classNumber FROM Classes WHERE facID = ( SELECT facID FROM Faculty WHERE name = 'John Smith' AND deptName = 'CST' ); ``` #### Explanation The issue with the above query is that the subquery can return more than one facID since there are multiple faculty members named "John Smith." This causes the main query to fail because it expects a single value for facID. #### Corrected SQL Query To fix this issue, we should use the `IN` operator instead of `=` to handle multiple values returned by the subquery: ```sql SELECT classNumber FROM Classes WHERE facID IN ( SELECT facID FROM Faculty WHERE name = 'John Smith' AND deptName = 'CST' ); ``` By using `IN`, we ensure that the query works correctly even if there are multiple faculty members named "John Smith." #### Conclusion In situations where subqueries might return multiple results, it's important to choose the appropriate operator to handle those results. Using `IN` instead of `=` can prevent errors when dealing with potential multiple matches.
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