WebEnabled Decision Support Systems Queries Building Application Foundation

Web-Enabled Decision Support Systems Queries: Building Application Foundation Prof. Name Position University Name name@email. com (123) 456 -7890 1

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 2

Introduction v A database query is a question posed against database tables – A set of instructions – Enable us to present a unified view of data § From single or multiple tables – When executed, operate on database tables to output the query result § Single Number (aggregate query) § Record Set (select query) v Built using: – Graphical query design grid (Query By Example, QBE) – Standard Query Language (SQL) statements 3

Introduction (Cont. ) v Access queries can be broadly classified into three function-based categories: – Select queries – Special purpose queries (Crosstab, Parameter, and Make-Table queries) – Action queries (Update, Append, and Delete queries) The Access Query Menu 4

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 5

Working With Select Queries v Select Queries – Most common type of query used in database applications – Extract and output recordsets that satisfy specific selection criteria: § Arithmetic expressions § Logical expressions – Composed of three types of operations: § Projection operations § Selection operations § Sorting operations 6

Projection v Projection is a vertical slicing of an input recordset – Used to display one or more selected fields of a table – Example: § Input recordset: Student table § Output recordset: Name, Email, and DOB fields The Projection Operation 7

Selection v Selection is a horizontal slicing of an input recordset – Used to select one or more records (rows) that satisfy specified selection criteria – Example: § Input recordset: Student table § Selection criteria: Type = “Full Time” The Selection Operation 8

Sorting v Sorting provides an ordered sequence of an input recordset – Example: § Input recordset: Student table § Sort: Student. ID (ascending) The Sorting Operation 9

Creating a Query in the Design View v The Design View and Simple Query Wizard are the two most frequently used options for creating queries v How-to: Create a New Query Using Design View 1. Select the Queries option in the Objects Bar to display the two popular options for creating a new query. “Create Query” Options 10

Creating a Query in the Design View (cont. ) 2. Double-click on the Create query in Design View option to open a new query in the Design View. New Query Dialog Box 11

Query Design View v The Query Design View is divided into two halves: – The upper half, called a Table Pane, displays all the fields from the desired query tables – The lower half, the Design Grid, holds the table fields on which we would like perform Projection, Selection, and/or Sorting operations The Query Design View 12

A Select Query Example v Query: – “List the students’ information (Student. ID, Name, and Email) for all full time, freshman students sorted in descending order of their names. ” v Steps: 1. Projecting student identification number, name, and email columns 2. Selecting only full time, freshman students 3. Sorting selected records in descending order of student names 13

Projecting Student’s Contact Information v How-to: Build a Select Query 1. Open the university database and create a new query in the Design View. 2. Select the table tbl. Student and click the Add button to add it to the query design. 3. Click Close to exit the Show Table dialog box. 4. Add the Student. ID, Name, and Email fields to the Design Grid. Projecting Fields of the Student Table 14

Saving and Executing a Query v How-to: Build a Select Query (cont. ) 5. Save this query as “Qry. Selection” and run the query to verify the Projection operation. § To save, choose File | Save from the Main menu. § To run, choose Query | Run from the Main menu. 15

Selecting Freshman and Fulltime Students v How-to: Build a Select Query (cont. ) 6. Add =“Freshman” criterion for the Class column and =“Full Time” criterion for the Type column in the Criteria row. 7. Uncheck the check boxes in the Show row for the Class and Type columns. 8. Save and run the query to verify Selection operation. Selecting Rows of the Student Table 16

Sorting Student’s Records v By default, query results are displayed in the same order in which they appear in the table v How-to: Build a Select Query (cont. ) 9. Choose the “Descending” order using the drop-down list in the Sort row of the Name column. Sorting Student Records in Descending Order by Student Names 17

Query Output v How-to: Build a Select Query (cont. ) 10. Save and run the query to verify Selection operation. Output of the Example Select Query 18

Moving or Removing Fields and Tables in Design View v By default, the order of the columns in the Design Grid is the order of the columns in the query result v Moving columns in the Design Grid: – Select the entire column and drag it to the desired location. v Removing columns from the Design Grid: – Select the entire column and hit the Delete button. v Removing tables from the Table Pane: – Select the table by clicking on the table list and then remove it by hitting the Delete button. – Removes the corresponding columns of that table from the Design Grid. 19

Exploring Query Toolbar and Menus 20

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 21

Queries with Multiple Tables (The Join Operation) v Queries can systematically join multiple tables to create a unified view of the fragmented data v Join operations involve adding multiple tables to the Table Pane – Combine with projection, selection, and sorting operations to create more complex queries The Join Operation 22

Hands-On Tutorial: Working with Join Queries v Query: – “List the student information (Student. ID and Name) and name of their departments (not the Dept. ID). ” v How-to: Design a Query that Involves Multiple Tables 1. Open the university database and start with a new query in the Design View. Add the tbl. Student and tbl. Department to the Table Pane. 2. Add the required fields to the Design Grid. Joining Student and Department Tables in the Design View 23

Hands-On Tutorial: Working with Join Queries (cont. ) 3. Save the query as “Qry. Join. Query” and run it. The Join Result in the Datasheet View 24

The Join Operation v The join operation takes two distinct recordsets as an input and produces a single output recordset, referred as the join result – Each record from the first recordset is joined with all records in the second – The join result filters these joined records via the join condition v An inner join is based on an equality condition of primary key-foreign key columns – Default join type – Join results will include records from both the tables which satisfy the primary key-foreign key conditions – When adding related tables to the Table Pane, Access automatically displays such relationships 25

The Join Operation (cont. ) v Outer joins include all the records from one table and only those records from the other table where joined fields are equal – Left outer joins include all records in the left table § Default outer join type – Right outer joins include all records in the right table v If the two tables added to the Table Pane to join are not related to each other, no join condition is used in the join operation – Join result in an all-to-all join (or Cartesian product join) – Each record from the first input recordset is joined with all the records from the second input recordset 26

Join Properties v We can view and alter join types using the Join Properties dialog box – To invoke the Join Properties dialog box, right-click the relationship line in the Table Pane and choose Properties from the short-cut menu. Selecting a Join Type in Join Properties Dialog Box 27

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 28

Working with Operators v In Access, we have an option to use different operators in the query design to build conditional statements v Most commonly used operators: – Comparison operators – Logical operators – BETWEEN operator – LIKE operator 29

Comparison Operators v We use comparison operators to select a specific group of records from a table – Operators: § >, >=, <, <=, =, != v Examples: – Credit. Hours > 3. 0 – Year = 2002 30

The Logical Conditions v We need logical operators to combine multiple criteria – Operators: § AND, OR, and NOT v Examples: – Salary > 7000 AND Salary < 10000 – Class = “Sophomore” OR Class = “Freshman” – Class = “Sophomore” AND Type = “Full Time” 31

The BETWEEN Operator v We use the BETWEEN operator along with the logical AND operator to specify an inclusive range between two values – For use with text, numeric, or date fields v Examples: – BETWEEN #1/1/95# AND #1/1/2002# – BETWEEN 70, 000 AND 100, 000 32

The LIKE Operator and Wildcard Character v The LIKE operator finds groups of potentially related items v It is often used with the wildcard character, the asterisk (*) v Examples: – LIKE “*Computer*” § Text includes “Computer” – LIKE “Applied*” § Text begins with “Applied” 33

Working with Dates v We use the pound sign (#) to represent the data type v Access has many built-in functions to handle dates and times data types v Example: – <= #1/1/2001# § Everything on and before January 1, 2001 – < Now() § Everything before current date 34

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 35

Hands-On Tutorial: A Select Query with Join of Multiple Tables v Query: – “List the contact information (name, email, and address) for all Industrial Engineering (ISE) students who have taken any computer- or databaserelated courses in the last six years and earned a grade point average of 3. 5 or better in these courses. Sort the list in descending order of student’s letter grade. ” v Tables: – Student table – Transcript table – Section table – Course table 36

Hands-On Tutorial (cont. ): A Select Query with Join of Multiple Tables v How-to: Write a Complex Query using the Projection, Selection, Sorting, and Join Operations 1. Open the university database and start with a new query in the Design View. Add the required four tables to the Table Pane. 2. Add the required fields from their respective tables to the Design Grid. A Select Query Design with Multiple Tables 37

Hands-On Tutorial (cont. ): A Select Query with Join of Multiple Tables 3. Add the criteria >= 3. 5 for the Grade column. Specify the expression =“ISE” for the Dept. ID field. § Save and run the query to verify the design so far. 4. Assign the expression > Year (Now ()) - 6 in the Year field. A Select Query Design with Multiple Tables 38

Hands-On Tutorial (cont. ): A Select Query with Join of Multiple Tables 5. Place the final expression Like “*computer*” Or Like “*database*” in the course name field. 6. Use the Sort row to specify descending order for the Grade column. 7. Use the Show row to display only the Name, Address, and Email columns. Uncheck all other columns in the Show row. 8. Save and run the query. 39

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 40

Using Total Row (The Group. By Operation) v The Group. By operation puts together records based on some similarity criteria and treats them as one unit or a group – Extensively used to furnish data summaries – Allows us to apply aggregate functions to the set of records 41

Hands-On Tutorial: Using the Total Row v Query: – “Determine the total number of students in each department. ” v How-to: Create a Totals (or Group. By) Query 1. Open the university database and start with a new query in the Design View. Add the student and department tables. 2. Add the student ID and department name fields to the Design Grid. 3. Designate this query as a Totals query by clicking on the Totals button on the toolbar. 4. Click in the Total row under the Student. ID column, and select the Count option from the drop-down list of aggregate functions. 42

Hands-On Tutorial: Using the Total Row (cont. ) 5. The Design View should appear as below: Grouping Student Records by Department in the Design View 43

Hands-On Tutorial: Using the Total Row (cont. ) 6. Save and run the query for the result shown below. § Aggregation fields (like Student. ID in this example) are named as <aggregation>Of<field name>. 7. Rename the Student. ID count column as “Total. Students: Student. ID”. The Output of Group. By Operation 44

Hands-On Tutorial: Using the Total Row with the Where Clause v Query: – “List the course information for those courses whose average evaluation was better than 80 points in the last 5 years. ” v How-to: Create a Total Query Using the Where Clause in the Total Row 1. Open the university database and start with a new query in the Design View. Add the course and section tables. 2. Add the Name field from the course table and the Evaluation and Year fields from the section table to the Design Grid. 3. Designate this query as a Total query by clicking on the Totals button on the toolbar. 45

Hands-On Tutorial (cont. ): Using the Total Row with the Where Clause 4. Click on the Total row under the Evaluation column, and select the Average option from the drop-down list of aggregate functions. 5. Add selection criteria (> Year (Now ()) - 5) using the Where option under the Year column. 6. Specify the selection criteria (>80) for the Evaluation column. 7. Remove the check in the Show row for the Year column. 8. Save the query as “Qry. Course. Evaluation” and run it. The Query Output 46

Hands-On Tutorial (cont. ): Using the Total Row with the Where Clause – The final Design View is shown below: The Total Row with the Where Clause 47

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 48

Creating Calculated Fields v Access queries allow us to create calculated fields as a part of the query design – Used to represent derived attributes § Attributes that are calculated using other attributes of the relation – Expressed as a new field in separate column of the query Design Grid § Instead of adding a column from the Table Pane, we write an expression in the Design Grid that, when evaluated, gives the value of the field § Existing field names are enclosed in square brackets [ ] to distinguish them from other entries in the expression – Example: § Age: Now() – [Date. Of. Birth] 49

Hands-On Tutorial: Creating Calculated Fields v Calculated Field: – Grade Point Average (GPA) § Calculated by first summing the product of the grade point and corresponding credit hours and then averaging it over the total number of credit hours earned v How-to: Create the Calculated Fields in Access Queries 1. Open the university database and start with a new query in the Design View. Add required tables to the Table Pane. 2. Add the student Name, Student. ID, and Credit. Hours fields to the Design Grid. 3. Click the Total button on the toolbar and select the Sum aggregate function in the Total row of the Credit. Hours column. Rename this column as TC: Credit. Hours. 50

Hands-On Tutorial: Creating Calculated Fields (cont. ) 4. Add the calculated field TG: [Credit. Hours]*[Grade]. Choose the Sum aggregate in the Total row. 5. Add another calculated field, GPA: [TG]/ [TC]. Assign an Expression option in the Total row for this column. Creating Calculated Fields for GPA Calculations 51

Calculated Fields with Strings v We can also perform string operations on fields v Example: – Name: [First. Name] & “ ” & [Last. Name] § Obtains the full name by combining the first name and the last name § The ampersand (&) operator combines the string values from First. Name, Last. Name, and an empty string 52

Expression Builder v The Access Expression Builder dialog box simplifies the process of developing complicated expressions for calculated fields – To invoke the Expression Builder dialog box, click the Build button on the toolbar. The Expression Builder Dialog Box 53

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 54

Parameter Queries v A Parameter query is a query that prompts for parameter values and dynamically assigns user-entered values in the selection criteria to run the query – At each execution, users may enter different parameter values for the desired result v We create a Parameter query in the same manner we create a Select query – We specify one or more parameters of the query in the selection criteria using square brackets [ ] § Dept. ID = [ ] – To prompt the user with an appropriate message to enter parameter values, enclose the message in the square brackets § Dept. ID = [Please Enter Department Name] 55

Parameter Queries (cont. ) The Query Output The Parameter Query in the Design View 56

Hands-On Tutorial: Working with Parameter Queries v Query: – “Display a list of faculty members who have joined a particular college within a specified date range. ” v Tables: – tbl. College – tbl. Department – tbl. Faculty 57

Hands-On Tutorial: Working with Parameter Queries (cont. ) v How-to: Work with the Parameter Queries 1. Open the university database for a new query in the Design View. Add the college, department, and faculty tables to the Table Pane. 2. Add fields to the Design Grid as shown below. The Parameter Query with Multiple Parameters 58

Hands-On Tutorial: Working with Parameter Queries (cont. ) 3. Enter the “[Enter the College]” parameter for the College. ID column. Also, assign the “Between [Starting Date] And [Ending Date]” criteria under the Joining. Date column. 4. Save and run the query. The Parameter Query with Multiple Parameters 59

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 60

Crosstab Queries v Crosstab queries are used to group and summarize the information and display it in a spreadsheet format – Less repetition of information than in the Datasheet View – Easier to read analyze v Crosstab queries are defined by three fields: – Row-heading fields: Dept. ID – Column-heading fields: Class (one column for each distinct Class) – Value fields: Student. ID Output of a Crosstab Query 61

Hands-On Tutorial: Working with Crosstab Queries v Query: – “For all the courses in the Computer Science department, we would like to display the total student enrollment in the Fall, Spring, and Summer semesters. ” v Fields: – Row-heading fields: Course Names – Column-heading fields: Sem – Value fields: Student. ID 62

Hands-On Tutorial: Working with Crosstab Queries (cont. ) v How-to: Work with Crosstab Queries 1. Open the university database with the new query, and add the course, section, and transcript tables to the Table Pane. 2. Add the Course. ID, Name, and Dept. ID fields from the course table, the Student. ID field from the transcript table, and the Sem field from the section table. 3. Change the type of query from the default Select query to the Crosstab query by choosing the Query | Crosstab Query item from the Main menu. 4. Select the Row Heading option for the Course. ID and Name columns in the Crosstab row. 63

Hands-On Tutorial: Working with Crosstab Queries (cont. ) 5. Select the Column Heading option for the Sem field. 6. Select the Value option for the Student. ID field. Also choose the Count function in the Total row for the Student. ID column. 7. Specify the department selection criteria (=“CISE”) under Dept. ID column. The Crosstab Query (Students per Semester per Course) in the Design View 64

Hands-On Tutorial: Working with Crosstab Queries (cont. ) 8. Save and then run the query to produce the result shown: The Output of the Crosstab Query (Students per Semester per Course) 65

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 66

Action Queries v Queries that can alter data by performing actions are called action queries – Allow us to modify a large number of records without having to write any special programs – Does not return a recordset – Three Types: § Update queries modify the values of one or more fields in the table § Delete queries use criteria to delete one or more records from the table § Append queries append one or more records to an existing table 67

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 68

Update Queries v An update query is an action query that can change field values in an existing table – Primarily update existing values in the database fields – Example: § Increase the Salary field of the faculty table by 5% Faculty Table After Faculty Table Before 69

Update Queries (cont. ) v We can select the records we would like to update by specifying update criteria – Example: § “Raise the salary for faculty members who joined the university before 1995 and have a salary of less than $70, 000. ” The Update Query in the Design View 70

Hands-On Tutorial: Working with an Update Query v Query: – “Update the Salary field in the faculty table for those faculty members who joined the university before 1995 and have a salary less than $70, 000. ” v How-to: Work with Update Queries 1. Open the university database and begin with a new query in the Design View. Add the faculty table to the query design. 2. Change the query type to the Update query. 3. Add the Salary and Joining. Date fields from the table list to the Design Grid. In the Salary field, enter the expression [Salary]*1. 05 under the Update To row. 71

Hands-On Tutorial: Working with an Update Query (cont. ) 4. In the Joining. Date field, specify the following criteria: “< #1/1/1995#”. In the Salary field, enter the criteria: “< 70, 000”. 5. Save the query as “Qry. Salary. Updates” and run it using the Run button on the toolbar. Click Yes when Access flashes a warning message. Access’ Update Warning 72

How to Preview Records that the Action Query Alters v When we run action queries, the changes made to the database tables are irreversible – It is important that we preview the exact changes that will occur § To preview, click the View button on the toolbar at the top left corner of the Database Window. § This opens a Datasheet View with records that the action query will alter. Preview of an Update Query in the Datasheet View 73

How Cascade Updates Work with Update Queries v What happens when we update the primary key of a table that is a foreign key in some other table and vice versa? – Update primary key: § Access allows us to update the primary key value § If the Cascade Updates option is selected, then Access automatically updates the foreign key value to maintain referential integrity – Update foreign key: § Access warns us for referential integrality constraint violations § If we continue with this update, we leave data in an inconsistent state The Cascade Update Error 74

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 75

Delete Queries v A delete query is an action query that deletes records from existing tables – Allow us to delete specific groups of records by applying deletion criteria to the appropriate fields The Delete Query in the Design View Preview of the Delete Query Displaying Records to be Deleted 76

Hands-On Tutorial: Building a Delete Query v Query: – “Delete the Industrial Engineering student records for those students who have recently graduated (i. e. , say all of the senior class). ” v How-to: Work with Delete Queries 1. Open the university database and start with the new query in the Design View. Add the student and department tables to the query design. 2. Change the query type from the default Select query to the Delete query. 3. Add the Class and Dept. ID fields from the student and department lists, respectively, to the Design Grid. 77

Hands-On Tutorial: Building a Delete Query (cont. ) 4. Add all fields from the student tables by adding an asterisk (*) to the Design Grid. 5. Specify the criteria fields for Class as = “Senior” and for Dept. ID as = “ISE”. 6. Save the query as “qry. Del. Students”. Preview the deleted records using the View button on the toolbar. The Delete Query in the Design View 78

Caution with Cascade Delete Option v Access performs cascade deletes when the delete query removes records that contain primary key values – Cascade deletes often increase the danger of massive data loss – Should be used with caution 79

Append Queries v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 80

Append Queries v An append query is an action query that copies records from one or more tables and adds them at the end of another table – Example: § “Retrieve the contact information and the date of birth of students in the College of Engineering and append them to a temporary table in the database for further processing. ” Append Query in the Design View Preview of the Append Query 81

Hands-On Tutorial: Building an Append Query v Query: – “Select the contact information and birthdates for all students in the College of Engineering and append them to a temporary table, tbl. Student. Archive, in the database for further processing. ” v How-to: Work with Append Queries 1. Start with a new query and add the student, department, and college tables to the query design. 2. Change the query type to the Append query to display the Append dialog box. Select the tbl. Student. Archive table from the drop-down list. The Append Dialog Box 82

Hands-On Tutorial: Building an Append Query (cont. ) 3. Add all the required fields and the selection criteria as shown below. 4. Save the query as “Qry. Student. Archive”. Preview the records selected to append to the archive table and run the query. Append Query in the Design View 83

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 84

In-Class Assignment v Consider the Bottling. mdb database, the database of a soft drink bottling plant. – The database manager has observed several defects in production. – The quality expert wants to investigate whethere is a relationship between bottle characteristics (such as material and size) and the number of defects. 1. Create a query that, for each type of material and bottle size, calculates the sum of the fraction of nonconforming bottles (the fraction is the ratio of the number of defective bottles to the total number of bottles). Title the query, “Qry. Materials”. Are there any trends? 2. Create a query that, for each type of drink, displays the sum of the fraction of nonconforming bottles. Title the query, “Qry. Drink. Type”. Are there any trends? 85

Overview v 8. 1 Introduction v 8. 2 Working with Select Queries v 8. 3 Queries with Multiple Tables (The Join Operation) v 8. 4 Working with Operators v 8. 5 Hands-On Tutorial: A Select Query with Join of Multiple Tables v 8. 6 Using Total Row (The Group. By Operation) v 8. 7 Creating Calculated Fields v 8. 8 Parameter Queries v 8. 9 Crosstab Queries v 8. 10 Action Queries v 8. 11 Update Queries v 8. 12 Delete Queries v 8. 13 Append Queries v 8. 14 In-Class Assignment v 8. 15 Summary 86

Summary v A query is a question posed against database tables. v Access allows us to build queries using a graphical query grid (Queryby-Example or QBE) and by writing SQL statements. v Access queries can be broadly classified into three function-based categories: – Select Queries – Special Purpose Queries (Crosstab, Parameter, and Make-Table queries) – Action Queries (Update, Append, and Delete queries) v Select queries are the most common type of query used in database applications. – A Select query selects or extracts data from one or more existing tables and displays the selection in the Datasheet View. 87

Summary (cont. ) v Query Operations: – – – v Projection is a vertical slicing of a recordset. Selection is a horizontal slicing of a recordset. Sorting provides an ordered sequence of a recordset. Join is a vertical merging of two tables. The Group. By operation places similar records together and treats them as one unit or group. A parameter query prompts user for criteria values when the query is executed. – The input values are then used in the selection criteria to run the query. v We use crosstab queries to group and summarize information and display it in a spreadsheet format. – Create less repetition of information in the datasheet, making it easier to read analyze the selected field data. 88

Summary (cont. ) v Access queries are not restricted to data retrieval v Queries that can alter data by performing actions are aptly called action queries: – Update queries modify the values of one or more fields in the table. – Delete queries use criteria to delete one or more records from the table. – Append queries append one or more records to an existing table. 89

Additional Links v Review more sample Access Queries from database files on the book website: http: //www. dssbooks. com. v Refer MS Access 2003: The Complete Reference by Virginia Andersen for more details on Access Queries. v Also refer Access 2003 Bible by Cary N. Prague, Michael R. Irwin, and Jennifer Reardon. v Also see: http: //msdn. microsoft. com/ for useful tips on Access Queries. 90