1. Working With Databases
Chapter 10
Working With Databases

2. Chapter 10 Introduction

3. Chapter 10 Topics Basic database terminology
Fundamental database concepts
Use ADO .NET to access databases
Display, sort, and update database data
Use the DataGridView control

4. Section 10.1 What Is a Database?
A Database is a Collection of Data Organized in Tables, Rows, and Columns

5. Terminology Database: a collection of interrelated tables
Table: a logical grouping of related data
A category of people, places, or things
For example, employees or departments
Organized into rows and columns
Field: an individual piece of data pertaining to an item, an employee name for instance
Record: the complete data about a single item such as all information about an employee
A record is a row of a table

6. Database Table Each table has a primary key
Uniquely identifies that row of the table
PartNumber is the primary key in this example
Columns also called fields or attributes
Each column has a particular data type
Row
(Record)
Column
Field

7. VB and Access Data Types
VB data types must match table data types
MS Access and VB have similar data types
Access Data Type Visual Basic Data Type
AutoNumber Long
Date/Time Date, DateTime
Number, Integer Integer
Number, long integer Long Integer
Number, single Single
Number, double Double
Text String
Yes/No Boolean

8. Database Design
A database schema is the design of tables, columns, and relationships between tables
Define a column for each piece of data
Allow plenty of space for text fields
For the members of an organization:
Column Name Type Size
First_Name Text 40
Last_Name Text 40
Phone Text 30
Text 40
Date_Joined Date/Time
Officer Yes/No 1

9. Issues with Redundant Data
Database design minimizes redundant data
In the following employee table:
ID First_Name Last_Name Department
Ignacio Fleta Accounting
Christian Martin Computer Support
Orville Gibson Human Resources
00300 Jose Ramirez Research & Devel
Ben Smith Accounting
Allison Chong Computer Support
Same dept name appears multiple times
Requires additional storage space
Causes problems if misspelled
What if a department needs to be renamed?

10. Eliminating Redundant Data
Create a department table
Dept_ID Dept_Name Num_Employees
1 Human Resources 10
2 Accounting 5
3 Computer Support 30
4 Research & Development 15
Reference department table in employee table
ID First_Name Last_Name Dept_ID
Ignacio Fleta 2
Christian Martin 3
Orville Gibson 1
Jose Ramirez 4
Ben Smith 2
Allison Chong 3

11. One-to-Many Relationships
The previous changes created a one-to-many relationship
Every employee has one and only one dept
Every department has many employees
DeptID in department table is a primary key
DeptID in employee table is a foreign key
In general, a one-to-many relationship is created when the primary key of one table is specified as a field of a another table

12. Section 10.2 Using the DataGridView
The DataGridView Control Allows you to Display a Database Table in a Grid Which Can be Used at Runtime to Sort and Edit the Contents of the Table

13. Connecting VB to a Database
VB provides tools to display database tables
Data binding links tables to form controls
Controls called components establish the link
A wizard guides you through the process
We’ll use these data-related components:
Data source – usually a database
Binding source – holds database name, location, and other connection information
Table adapter – uses SQL to select data
Dataset – in-memory copy of data from tables

14. Connecting VB to a Database
The flow of data from database to application
Note that data moves in both directions
Data travels from data source to application
Application can view/change dataset contents
Changes to dataset can be written back to the data source
Tutorial 10-1 demonstrates how to connect a database table to a DataGridView control
Data Source
Binding Source
Table Adapter
Dataset
Application

15. Section 10.3 Selecting Dataset Rows
Visual Basic Provides Convenient Tools for Selecting Which Rows from the Dataset You Want to Display

16. Structured Query Language (SQL)
Often need to select certain rows in a table using Structured Query Language (SQL)
Standard method of working with a database
Adopted by most all database software
Not a general purpose programming language
Defines how to construct queries that return selected data from the database

17. SQL Query Example
You might want to select all employees hired before 1998 and earning less than $45,000
Select ID, Name, Full_Time, Hire_Date, Salary From employees Where Hire_Date < 1/1/1998 and Salary < 45000
Select, From, and Where are keywords
Fields to be returned listed after Select
Table containing the data listed after From
Conditions affecting row selection after Where
SQL query is a property of the TableAdapter

18. Configuring the TableAdapter
Right-click on dataset and select Configure to start TableAdapter Configuration Wizard
Can modify a simple query directly in wizard
Or use Query Builder for more complex query
Query Builder is a tool to create or modify queries with minimal knowledge of SQL
To add a query to a DataGridView
Right-click Table Adapter icon attached to grid
Select Add Query from shortcut menu
Tutorial 10-2 demonstrates how this is done

19. Section 10.4 Data-Bound Controls
Some Controls Can Be Bound to a Dataset. A Data-bound Control Can be Used to Display and Edit the Contents of a Particular Row and Co.lumn

21. Advantages of Data-Binding
Can add multiple data sources to a project
Can bind fields in a data source to controls:
Text boxes
Labels
List boxes
Contents of data-bound controls change automatically when moving from row to row
Updating the contents of a database field from a data-bound control is also very easy

22. Binding Existing Dataset to DataGrid
Use the Data Sources window
Locate the dataset table
Drag table to an open area of a form
Creates a data grid bound to the data source
Automatically adds a navigation bar to form
Set Dock property to Center Docking to make the data grid fill the entire form

23. Binding Individual Fields to Controls
Use the Data Sources window
Locate the dataset table
Select Details from the table drop-down list
Drag table to an open area of a form
Creates a separate control for each field
Can also drag columns individually
Adds automatic navigation bar as before
Text and numeric fields added as text boxes
Yes/No fields added as checkboxes
May wish to change some control properties

24. Binding to List and Combo Boxes
List and combo boxes are frequently used to supply a list of items for a user to select from
Such lists are often populated from a table
Must set two list/combo box properties
DataSource identifies a table within a dataset
DisplayMember identifes the table column to be displayed in the list/combo box
If table column dragged onto a list/combo box
Visual Studio creates the required dataset, table adapter, and binding source components
Tutorial 10-3 shows this type of binding

25. Adding New Rows to a Dataset
NewRow method creates a new, empty row
Assign values to columns in the empty row
Add method appends new row to the dataset
The following example adds a new row to the Payments table of the dsPayments dataset
Dim row as dsPayments.PaymentsRow
Row = CType(DsPayments.Payments.NewRow(), _
dsPayments.PaymentsRow)
With row
row.Member_ID = 5
row.Payment_Date = #5/15/2006#
row.Amount = 500D
End With
DsPayments.Payments.Rows.Add(row)

26. Another Means to Add Dataset Rows
Can call the dataset Add method directly
This approach is more straightforward but:
Must specify values in correct column order
Previous example becomes far simpler:
DsPayments.Payments.Rows.Add( _
Nothing, 5, #5/15/2006#, 500D)
Payments table 1st column is autonumber so:
Must have an argument for this column
Pass Nothing as the value for this column

27. Removing a Row from a Dataset
Two steps to remove a row
Get a reference to the row to remove
Call Remove method on Rows collection
Following example calls FindByID with the primary key to get a reference to the row
Dim row as DataRow = _ DsPayments.Payments.FindByID(36) DsPayments.Payments.Rows.Remove(row)

28. Updating the Database
Previous add and remove examples change the dataset but not the underlying database
Must call TableAdapter Update method to save dataset changes to the database
To write changes in the DsPayments dataset to the underlying database:
PaymentsTableAdapter.Update(DsPayments)
Tutorial 10-4 demonstrates adding new rows to the Payments table

29. Reading Dataset Rows with For-Each
A For-Each statement can be used to iterate over all rows of a dataset
Usually use a strongly typed dataset for this
Sum Amount column of dsPayments dataset
Dim row as dsPayments.PaymentsRow
Dim decTotal as Decimal = 0
For Each row in DsPayments.Payments.Rows
decTotal += row.Amount
Next
Tutorial 10-5 demonstrates this technique

30. Section 10.5 Structured Query Language (SQL)
SQL Is a Standard Language for Working With Databases

31. The Select Statement
Select retrieves rows from one or more tables in a database
Basic form of Select for a single table is
Select column-list
From table
column-list contains column names to select from table, each separated by a comma
The following Select statement retrieves the ID and Salary fields from the SalesStaff table
Select ID, Salary
From SalesStaff

32. Column Names Use asterisk to select all columns in a table
From SalesStaff
Unlike VB names, SQL columns can have embedded spaces
If so, use square brackets around column names
Select [Last Name], [First Name]
Better to avoid embedded spaces for this reason
As operator can be used to rename columns
Select Last_Name, Hire_Date As Date_Hired

33. Creating New Columns
Sometimes useful to create a new column by appending existing columns together
Create a Full_Name field from first and last name
Select Last_Name + ‘, ‘ + First_Name as Full_Name
From SalesStaff
Creates a Full_Name field in the format last, first
Can also be useful to create a new column by performing arithmetic operations
Columns involved must be numeric
Select ID, hrsWorked * hourlyRate As payAmount
From Payroll
Creates a payAmount column with gross pay

34. Sorting Rows with Order By Clause
SQL Select has an optional Order By clause that affects the order in which rows appear
Order by Last_Name, First_Name
Displays rows in order by last name, then first
Sort in reverse order (high to low) using Desc
Order by Last_Name DESC
Order By clause appears after From clause
Select First_Name, Last_Name, Date_Joined
From Members
Order By Last_Name, First_Name
Lists all members by last name, then first

35. Selecting Rows with Where Clause
SQL Select has an optional Where clause that can be used to select (or filter) certain rows
Where Last_Name = ‘Gomez’
Displays only rows where last name is Gomez
Must be a defined column (in table or created)
This example selects based on a created field
Select Last_Name, hrsWorked * Rate As payAmount
From Payroll
Where payAmount > 1000
Order by Last_Name
Selects those being paid more than $1,000

36. SQL Relational Operators
SQL Where uses relational operators just like a VB If
Operator Meaning
= equal to
<> not equal to
< less than
<= less than or equal to
> greater than
>= greater than or equal to
Between between two values (inclusive)
Like similar to (match using wildcard)
Example of Between operator:
Where Hire_Date Between #1/1/1992# and #12/31/1999#
Example of Like operator with % sign as wildcard:
Where Last_Name Like ‘A%’

37. Compound Expressions
SQL uses And, Or, and Not to create compound expressions
Select all employees hired after 1/1/1990 and with a salary is greater than $40,000
Where (Hire_Date > #1/1/1990#) and (Salary > 40000)
Select all employees hired after 1/1/1990 or with a salary is greater than $40,000
Where (Hire_Date > #1/1/1990#) or (Salary > 40000)
Select employee names not beginning with A
Where Last_Name Not Like ‘A%’

38. Section 10.6 Karate School Management Application
Create an Application that Works With the Karate School Database