Mark Dixon, SoCCE SOFT 131Page 1 18 – Structured Query Language

Mark Dixon, SoCCE SOFT 131Page 2 Session Aims & Objectives Aims –To introduce the fundamental ideas involved in using SQL Objectives, by end of this week’s sessions, you should be able to: –Use SQL in your programs to create more complex record-sets

Mark Dixon, SoCCE SOFT 131Page 3 Example: People Database Person PersonIDSurnameForenamesGenderPhone 1DixonMarkYes SmithJohnYes JonesSallyNo BloggsFredYes AndersonGennyNo SmithBobYes01752

Mark Dixon, SoCCE SOFT 131Page 4 Example: People v1 Display Surname of all people in list box: Option Explicit Const cs = "Provider … " Private Sub Form_Load() Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "Person", cs lstPeople.Clear Do Until rs.EOF lstPeople.AddItem rs.Fields("Surname").Value rs.MoveNext Loop rs.Close Set rs = Nothing End Sub

Mark Dixon, SoCCE SOFT 131Page 5 Example: People v2 Display Surname of Male people in list box: Option Explicit Const cs = "Provider …" Private Sub Form_Load() Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "Person", cs Me.lstPeople.Clear Do Until rs.EOF If rs.Fields("Gender").Value = True Then lstPeople.AddItem rs.Fields("Surname").Value End If rs.MoveNext Loop rs.Close Set rs = Nothing End Sub

Mark Dixon, SoCCE SOFT 131Page 6 Example: People v3 Display Surname of Male people in list box: Option Explicit Const cs = "Provider …" Private Sub Form_Load() Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open " SELECT * FROM Person WHERE Gender = True ", cs Me.lstPeople.Clear Do Until rs.EOF lstPeople.AddItem rs.Fields("Surname").Value rs.MoveNext Loop rs.Close Set rs = Nothing End Sub SQL statement

Mark Dixon, SoCCE SOFT 131Page 7 SQL: Queries main purpose of databases: –get information back out: searching Structured Query Language –dedicated to interacting with databases 3 rd Generation Language (such as VB, C++) –code describes how to do task 4 th Generation Language (such as SQL) –code describes what to do (not how to do it)

Mark Dixon, SoCCE SOFT 131Page 8 SQL: SELECT statement SELECT statement –used to get data –can be embedded in VB, via rs.Open: rs.Open "Person", cs rs.Open "SELECT * FROM [Person]", cs all fields

Mark Dixon, SoCCE SOFT 131Page 9 SQL: WHERE & ORDER BY WHERE clause –used to restrict data SELECT * FROM [People] WHERE [age]>=18; ORDER BY clause –used to change order of data SELECT * FROM [People] ORDER BY [Surname];

Mark Dixon, SoCCE SOFT 131Page 10 SQL: strings (text data) Possible confusion: SELECT * FROM Person WHERE Surname = Smith this will look for field called Smith - gives error need single (SQL) quotes to signify literal text SELECT * FROM Person WHERE Surname = 'Smith'

Mark Dixon, SoCCE SOFT 131Page 11 SQL & MS access queries MS Access –Queries: select data from database –really SQL select statements –can use queries to test SQL code MS Access: People.mdb

Mark Dixon, SoCCE SOFT 131Page 12 People Database (with Hobbies) IDSurnameForenamesPhone 1DixonMark SmithJohn JonesSally BloggsFred AndersonGenny01752 HobbyIDDescriptionPersonID 1Archery1 2Herpetology1 3Music1 4Football2 5Rugby2 6Hitting people with swords1 Hobby Person

Mark Dixon, SoCCE SOFT 131Page 13 SQL: Joining tables SELECT * FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID]; Two tables Matching records IDSurnameForenamesPhone HobbyIDDescriptionPersonID 1DixonMark DixonMark DixonMark DixonMark01752 people with swords1 2SmithJohn SmithJohn01752

Mark Dixon, SoCCE SOFT 131Page 14 SQL: Joining tables IDSurname 1Dixon Smith 2 SELECT [ID], [Surname] FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID];

Mark Dixon, SoCCE SOFT 131Page 15 SQL: DISTINCT records SELECT DISTINCT [ID], [Surname] FROM [Person], [Hobby] WHERE [Person].[ID] = [Hobby].[PersonID]; IDSurname 1Dixon 2Smith

Mark Dixon, SoCCE SOFT 131Page 16 Example: People v4 User controls what is displayed: Option Explicit Const cs = "Provider …" Private Sub optAll_Click() Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset rs.Open "Person", cs Me.lstPeople.Clear Do Until rs.EOF Me.lstPeople.AddItem rs.Fields("Surname").Value rs.MoveNext Loop rs.Close Set rs = Nothing End Sub Private Sub optMale_Click() ‘ You fill in this code. End Sub Private Sub optFemale_Click() ‘ You fill in this code. End Sub

Mark Dixon, SoCCE SOFT 131Page 17 Example: People v5 User controls what is displayed: –V4 has 38 lines –do same with 23 Option Explicit Const cs = "Provider …" Private Sub optAll_Click() ‘ You fill in this code. End Sub Private Sub optMale_Click() ‘ You fill in this code. End Sub Private Sub optFemale_Click() ‘ You fill in this code. End Sub