Enterprise Development
Using Visual Basic 6.0
Autumn 2002
Tirgul #8
‘Tirgul’ # 8
Objectives
• SQL Queries & Statements
• Useful SQL techniques
• DB Comparison
‘Tirgul’ # 8
retrieve All records
• SELECT * FROM Users
• Use Constants:
Public Const GET_ALL_USERS = "Select * From Users"
• Use inside Function:
Public Function GetAllUsers() As ADODB.Recordset
'...
Set RS = Connection.execute(GET_ALL_USERS)
'...
End Function
‘Tirgul’ # 8
retrieve Some fields
• SELECT UserID, UserName FROM Users
• Use Constants:
Public Const GET_USERS_FIELDS = "Select UserID, UserName” & _
“ From Users"
• Inside a function
Public Function GetUsersFields() As ADODB.Recordset
'...
Set RS = Connection.execute(GET_USERS_FIELDS)
'...
End Function
‘Tirgul’ # 8
Conditions
• SELECT UserID, UserName FROM
Users WHERE UserName = 'James‘
• SELECT UserID, UserName FROM
Users WHERE UserID < 10
• SELECT UserID, UserName FROM
Users WHERE UserID < 10 OR
UserName = 'James'
‘Tirgul’ # 8
Conditions
• Cannot build all string
Public Const GET_USER_BY_NAME =
"SELECT UserID, UserName FROM Users WHERE UserName = '"
• Use inside Function:
Public Function GetUserByName(strUserName As String) As
ADODB.Recordset
'...
Dim strQuery As String
strQuery = GET_USER_BY_NAME & strName & "'"
Set RS = Connection.execute(strQuery)
'...
End Function
‘Tirgul’ # 8
Sorting
• SELECT * FROM Users ORDER BY
UserName DESC
• SELECT * FROM Users ORDER BY
UserName
• SELECT * FROM Users ORDER BY
UserName ASC
• SELECT * FROM Users ORDER BY
UserName, UserID DESC
‘Tirgul’ # 8
Sorting
• Use Constants:
Public Const GET_USERS_ORDER_DESC =
"SELECT * FROM Users ORDER BY UserName DESC"
• Use inside Function:
Public Function GetUserOrderDesc() As ADODB.Recordset
'...
Set RS = Connection.execute(GET_USERS_ORDER_DESC)
'...
End Function
‘Tirgul’ # 8
Add records
• INSERT INTO Users VALUES (10,
'James Crowley', 'PASSWORD')
• INSERT INTO Users (UserName,
UserID) VALUES ('James Crowley', 10)
• INSERT INTO Users (UserName,
Password) VALUES ('James Crowley',
'PASSWORD')
‘Tirgul’ # 8
Add records
Little an Evil..
• Use Constants:
Public Const INSERT_USER = "INSERT INTO Users (UserID,” & _
UserName) VALUES (‘"
• Use inside Function:
No Return value
Public Function InsertUser(strUserID As String, _
strUserName As String)
'...
Dim strQuery As String
strQuery = INSERT_USER & strUserID & "'" & strUserName & "')"
Set RS = Connection.execute(strQuery)
'...
End Function
‘Tirgul’ # 8
Another option.
• Use Array:
Public Function InsertUser(UserDataArr)
'...
Dim strQuery As String
strQuery = INSERT_USER & UserDataArr(0) & "'" & UserDataArr(0) & "')"
Connection.execute(strQuery)
'...
End Function
Public Function InsertUser(UserDataArr)
'...
RS!UserID = UserDataArr(0)
RS!UserName = UserDataArr(1)
'...
End Function
‘Tirgul’ # 8
Update records
• UPDATE Users SET UserName =
'James Smith', Password =
'NEWPASSWORD' WHERE UserID =
10
• UPDATE Furniture SET Price = 10
WHERE ItemType = 'Cupboard'
‘Tirgul’ # 8
Update records
• Use Constants:
Public Const UPDATE_USER = "UPDATE Users SET UserName = ‘"
• Use inside Function:
Public Function UpdateUser(strUserName As String)
'...
Dim strQuery As String
strQuery = UPDATE_USER & strUserName & "'"
Connection.execute(strQuery)
'...
End Function
‘Tirgul’ # 8
Delete a record
• DELETE FROM Users WHERE UserID = 10
• DELETE FROM Furniture WHERE Price < 10
• TRUNCATE TABLE authors
TRUNCATE TABLE is faster and uses fewer system
and transaction log resources than DELETE
‘Tirgul’ # 8
SQL Transaction statements
• BEGIN TRANSACTION
• COMMIT TRANSACTION
• ROLLBACK TRANSACTION
‘Tirgul’ # 8
Transaction Use
Public Function Insert() As Boolean
Conn.BeginTrans
'Add
'Delete
'Update
If Err.Number <> 0 Then
Conn.RollBack
Insert = False
Exit Function
End If
Conn.Commit
End Function
‘Tirgul’ # 8
Commercial Databases
•
•
•
•
Access
– Simple yet useful
– For a single/double work stations
– Limit data size
MS SQL Server
– Very common
– Only Microsoft…
– Ease of use
– Time-to-market
Oracle
– More “Commercial”
– Known as a powerful tool
– Multi platform – Win/Unix/Linux
IBM DB2
– More “Commercial”
– Multi platform – Win/Unix/Linux
– Useful for IBM family & tools
‘Tirgul’ # 8