Write a query to display the average number of days a book is kept during a checkout (Figure P7.103). # Entity-Relationship Diagram (ERD) Explanation## Figure P7.56: The CH07_FACT ERDThis diagram represents the relationships among entities in a library system, including CHECKOUT, PATRON, BOOK, AUTHOR, and WRITES.### Entities and Attributes1. **CHECKOUT** - **Primary Key (PK):** Check_Num - **Foreign Keys (FK):** Book_Num (FK1), Pat_ID (FK2) - **Attributes:** - Check_Out_Date - Check_Due_Date - Check_In_Date2. **PATRON** - **Primary Key (PK):** Pat_ID - **Attributes:** - Pat_FName - Pat_LName - Pat_Type3. **BOOK** - **Primary Key (PK):** Book_Num - **Foreign Key (FK):** Pat_ID - **Attributes:** - Book_Title - Book_Year - Book_Cost - Book_Subject4. **AUTHOR** - **Primary Key (PK):** Au_ID - **Attributes:** - Au_FName - Au_LName - Au_BirthYear5. **WRITES** - **Primary Key (PK) and Foreign Key (FK):** Book_Num (PK, FK1), Au_ID (PK, FK2)### Relationships- **CHECKOUT and PATRON:** A one-to-many relationship, where each PATRON can have multiple CHECKOUT records, but each CHECKOUT is associated with a single PATRON. - **BOOK and CHECKOUT:** A one-to-many relationship, where each BOOK can have multiple CHECKOUT entries, but each CHECKOUT is for a single BOOK. - **PATRON and BOOK:** A one-to-many relationship, where a PATRON can checkout multiple BOOKS, but each BOOK is associated with one PATRON in this context. - **AUTHOR and WRITES:** A one-to-many relationship, where each AUTHOR can write multiple BOOKS, as represented by the WRITES table linking AUTHORS to BOOKS.### Diagram Symbols- **Solid lines** represent direct relationships.- **Dashed lines** indicate linking or associative tables.- **Crow's foot notation** represents cardinalities, illustrating the type of relationship (one-to-many or **Average Days Kept**21.29*Description*: This section displays the average number of days an item or service is retained. The value indicates that, on average, items are kept for approximately 21.29 days. There are no accompanying graphs or diagrams with this information.

Solution: Given, Schema structure is-

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Write a query to display the average number of days a book is kept during a checkout (Figure P7.103).

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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Concept explainers

Single Table

In a database management system, a single table is designed to obtain data of heterogeneous items. A single-table design with DynamoDB resolves the issue of raising multiple requests for the relevant data of an entity.

Question

Write a query to display the average number of days a book is kept during a checkout (Figure P7.103).

# Entity-Relationship Diagram (ERD) Explanation

## Figure P7.56: The CH07_FACT ERD

This diagram represents the relationships among entities in a library system, including CHECKOUT, PATRON, BOOK, AUTHOR, and WRITES.

### Entities and Attributes

1. **CHECKOUT**
- **Primary Key (PK):** Check_Num
- **Foreign Keys (FK):** Book_Num (FK1), Pat_ID (FK2)
- **Attributes:**
- Check_Out_Date
- Check_Due_Date
- Check_In_Date

2. **PATRON**
- **Primary Key (PK):** Pat_ID
- **Attributes:**
- Pat_FName
- Pat_LName
- Pat_Type

3. **BOOK**
- **Primary Key (PK):** Book_Num
- **Foreign Key (FK):** Pat_ID
- **Attributes:**
- Book_Title
- Book_Year
- Book_Cost
- Book_Subject

4. **AUTHOR**
- **Primary Key (PK):** Au_ID
- **Attributes:**
- Au_FName
- Au_LName
- Au_BirthYear

5. **WRITES**
- **Primary Key (PK) and Foreign Key (FK):** Book_Num (PK, FK1), Au_ID (PK, FK2)

### Relationships

- **CHECKOUT and PATRON:** A one-to-many relationship, where each PATRON can have multiple CHECKOUT records, but each CHECKOUT is associated with a single PATRON.

- **BOOK and CHECKOUT:** A one-to-many relationship, where each BOOK can have multiple CHECKOUT entries, but each CHECKOUT is for a single BOOK.

- **PATRON and BOOK:** A one-to-many relationship, where a PATRON can checkout multiple BOOKS, but each BOOK is associated with one PATRON in this context.

- **AUTHOR and WRITES:** A one-to-many relationship, where each AUTHOR can write multiple BOOKS, as represented by the WRITES table linking AUTHORS to BOOKS.

### Diagram Symbols

- **Solid lines** represent direct relationships.
- **Dashed lines** indicate linking or associative tables.
- **Crow's foot notation** represents cardinalities, illustrating the type of relationship (one-to-many or

**Average Days Kept**

21.29

*Description*: This section displays the average number of days an item or service is retained. The value indicates that, on average, items are kept for approximately 21.29 days. There are no accompanying graphs or diagrams with this information.

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