如何选择超过4条条件的记录

Question

Select records based on the criteria shown

Is there any way i can select records from MySQL based on this criteria apart using the many if else statements. Actually what i have in mind is below

if CurrentLevel.SelectedItem <> Nothing AND Programme.SelectedItem = Nothing AND Gender.SelectedItem = Nothing Then

myconnection.Open()
Dim SelCmd as SqlCommand = New SqlCommand("Select * From StudentsList Where CurrentLevel = '"& CurrentLevel.SelectedItem &"'",myconnection)

And I'll have to do it for all the possible outcomes. Which makes the code very lengthy and tiresome to write.

Is there a shorter way of performing this search because I'll perform another search with almost 16 criteria.

Answer 1

The question is not entirely clear to me. You won't need a new if statement for all the criteria. You can achieve this by modifying the SQL query itself. One of the main purpose of SQL is to get data that match certain criteria.

SELECT * FROM StudentsList WHERE `CurrentLevel` = "level" AND `gender` = "male" AND `programme` = "something"

The above SQL query should give you a basic idea. It will select the rows which have CurrentLevel as level, gender as male and programme as something only, the rest will be ignored.

EDIT:

I don't know VB. Here is a quick, dirty example in C# which will help you understand the basic logic behind this.

string sqlQuery = "SELECT * FROM StudentsList ";
if(currentLevelDropDown.SelectedItem.Text != "") 
{
    sqlQuery + "WHERE CurrentLevel = " + currentLevelDropDown.SelectedItem.Text;
}

if(ProgrammeDropDown.SelectedItem.Text != "")
{
    sqlQuery + " AND WHERE programme = " + ProgrammeDropDown.SelectedItem.Text;
}

//Final Query becomes: SELECT * FROM StudentsList WHERE CurrentLevel = userSelectedOption AND WHERE programme = userSelectedProgrammeOption

//Finally execute the sqlQuery