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Database Systems: Design, Implemen...

12th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781305627482

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Section
BuyFindarrow_forward

Database Systems: Design, Implemen...

12th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781305627482
Chapter 8, Problem 62P
Textbook Problem
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Write a query to display the patron ID and the average number of days that patron keeps books during a checkout. Limit the results to only patrons that have at least three checkouts. Sort the results in descending order by the average days the book is kept. (Figure P8.62)

FIGURE P8.62 AVERAGE DAYS KEPT BY PATRON

Chapter 8, Problem 62P, Write a query to display the patron ID and the average number of days that patron keeps books during

Program Plan Intro

SELECT statement:

It is used to retrieve information from the table or database. The syntax for the “SELECT” statement is given below:

Syntax:

SELECT * FROM table_Name;

“Round()” function:

This function is used to round a number that specified in decimal places. The format of the “Round()” function is as follows:

Syntax:

ROUND(number, decimal_places)

AVG function:

  • • It is one of the function of aggregate function.
  • • This function is used to get the average of all the values from the column.
  • Syntax: SELECT AVG(column_Name) FROM table_Name;

COUNT function:

  • • It is one function of the aggregate function.
  • • This is used to count the number of rows for the particular column.
  • • Syntax: SELECT COUNT(column_Name) FROM table_Name;

“GROUP BY” Clause:

The GROUP BY clause is used to group the result of a SELECT statement done on a table where the tuple values are similar for more than one column.

Syntax:

SELECT expression1, expression2, expression_n, aggregate_function (expression)FROM table_name WHERE conditions GROUP BY expression1, expression2, expression_n;

ORDER BY Clause:

SQL contains “ORDER BY” clause in order to sort rows. The values get sorted in ascending as well as descending order. The keyword used to sort values in ascending order is “ASC” and for descending order is “DESC”. By default, it sorts values by ascending order.

Syntax:

SELECT column_Name1, column_Name2 FROM table_Name ORDER BY column_Name2;

“HAVING” Clause:

The “HAVING” clause is used to restrict the groups that are included.

  • • This restriction does not apply to individual rows but relatively apply to groups.

Example:

The example for “HAVING” clause is given below:

SELECT STUDENT_ID, NAME, AGE, ADDRESS, TOTAL_MARK FROM STUDENTS GROUP BY AGE HAVING COUNT(AGE) >= 10;

  • • The above query is used to display a record for a similar age count that would be more than or equal to “10”.

Explanation of Solution

Query to display the patron ID and the average number of days from “CHECKOUT”:

The query to display the patron ID and the average number of days from “CHECKOUT” table which is given below:

SELECT PAT_ID, Round(Avg(CHECK_IN_DATE - CHECK_OUT_DATE), 2) AS "Average Days Kept" FROM CHECKOUT

GROUP BY PAT_ID

HAVING Count(CHECK_NUM) > 2

ORDER BY Round(Avg(CHECK_IN_DATE - CHECK_OUT_DATE), 2) DESC;

The above query was executed using the tool “Access 2013”.

Explanation:

  • • The above query is used to display the patron ID and the average number of days that patron keeps book from “CHECKOUT” table.
    • ○ From the given query, first compute the average number of days for each group of patron ID by using “GROUP BY” clause...

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Chapter 8 Solutions

Database Systems: Design, Implementation, & Management
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