加入兩個表

Question

st = "SELECT YearLevel FROM Students WHERE StudentID = " & txtStudentID.Text 
    da = New OleDbDataAdapter(st, conn) 
    da.Fill(ds, "Students") 
    YearLevel = ds.Tables("Students").Rows(0).Item("YearLevel") 

    st1 = "SELECT TuitionFee, BookFee, MiscellaneousFee, OtherFee FROM Expenses WHERE YearLevel = " & YearLevel 

    da1 = New OleDbDataAdapter(st1, conn) 
    da1.Fill(ds1, "Expenses") 

所以我有那個代碼，然後我有我的第二個查詢中缺少運算符的錯誤，可能的解決方案是什麼？

Answer 1

您會收到此錯誤消息，因爲YearLevel的值爲Grade 1，因此需要用引號將其轉義。所以，你希望你的RDBMS來執行實際的查詢可能看起來是這樣的：

SELECT TuitionFee, BookFee, MiscellaneousFee, OtherFee 
FROM Expenses 
WHERE YearLevel = 'Grade 1' 

您可以直接在字符串st1中添加引號，但是這可能讓門打開SQL注入。這裏是一個更加安全的方式去這樣做：

MyCommand = New SqlCommand("SELECT TuitionFee, BookFee, MiscellaneousFee, OtherFee FROM Expenses WHERE YearLevel = @YearLevel", conn) 
MyCommand.Parameters.AddWithValue("@YearLevel", YearLevel) 

VB.net應該感覺到參數是字符類型，並自動報價爲你逃避它。