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The Tables of a Database |
In the first lesson, we defined a database as one or more lists. A list in a database is called a table. The idea is that a table is an arrangement of the categories of information stored in a list and a table makes it easy to locate and manage the records of a list. To better explore lists, you should know how a table organizes its value. A table is made of one or more categories divided as columns. Consider the following example of a list of teachers of a high school:
Notice that the first named are grouped in a common category, so are the last names and so on. This makes it easy to locate a category and possibly a value.
To create a table, you start an expression with CREATE TABLE followed by the name of the table: CREATE TABLE Name; The CREATE and TABLE keywords must be used to create a table. The Name factor specifies the name of the new table.
After the CREATE TABLE expression, you must enter a name for the table. The name of a table can be very flexible. This flexibility can be overwhelming and confusing. To avoid these, there are suggestions and conventions we will apply when naming our tables:
Here is an example: Private Sub btnCreateTable_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnCreateTable.Click
Dim conADO As ADODB.ConnectionClass = New ADODB.ConnectionClass
Dim strCreate As String
conADO.Open("Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source='C:\Programs\SchoolRecords1.mdb'", Nothing, Nothing, 0)
strCreate = "CREATE TABLE Students . . .;"
conADO.Close
End Sub
After formulating the expression that creates the table, you can pass it to the Execute() method of a Connection variable. This would be done as follows: Private Sub btnCreateTable_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnCreateTable.Click
Dim conADO As ADODB.ConnectionClass = New ADODB.ConnectionClass
Dim strCreate As String
conADO.Open("Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source='C:\Programs\SchoolRecords1.mdb'", Nothing, Nothing, 0)
strCreate = "CREATE TABLE Students . . .;"
conADO.Execute(strCreate, 0, 0)
conADO.Close
End Sub
Besides the CREATE TABLE expression followed by a name, there are other issues related to creating a table. We will review more details in future lessons.
The tables of an ADO database are stored in a collection. To locate this collection, you can access the Tables property of the Catalog class of the ADOX namespace.
To remove a table from a database, create a DROP TABLE expression followed by the name of the table. The formula to use is: DROP TABLE TableName; Replace the TableName factor of our formula with the name of the table you want to delete. Here is an example: Private Sub btnDeleteTable_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnDeleteTable.Click
Dim conSchoolRecords As New ADODB.Connection
conSchoolRecords.Open("Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source='C:\Programs\SchoolRecords.mdb'")
conSchoolRecords.Execute("DROP TABLE Teachers;")
MsgBox("The Teachers table of the SchoolRecords database has been deleted.")
conADO.Close
End Sub
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