尽管在例如 Access 中工作，SQL 查询却没有提供任何结果？

Question

Here's the problem:

I'm working with Visual Studio and made a Winforms application. This is supposed to work with a database. Reading the database using a SQL Query works totally fine without any problems.

cmd.CommandText = 
     "SELECT Buecher.Bu_ISBN AS ISBN, 
             Buecher.Bu_Titel AS Titel,  
             Buecher.Bu_Originaltitel AS Originaltitel, 
             Buecher.Bu_Buchreihe AS Buchreihe, 
             Buecher.Bu_Genre AS Genre, 
             Autor.Au_Vorname AS [Autor-Vorname], 
             Autor.Au_Nachname AS[Autor-Nachname], 
             Verlag.Ve_Name AS Verlag 
      FROM ((((Buecher 
               INNER JOIN [Buch-Autor] 
                 ON Buecher.Bu_ID = [Buch-Autor].Bu_ID) 
               INNER JOIN Autor 
                 ON [Buch-Autor].Au_ID = Autor.Au_ID) 
               INNER JOIN [Buch-Verlag] 
                 ON Buecher.Bu_ID = [Buch-Verlag].Bu_ID) 
               INNER JOIN Verlag 
                 ON [Buch-Verlag].Ve_Name = Verlag.Ve_Name)";
        ausgabe();

(it is in German, ausgabe() is a method that transfers the Query into a DataGridView - works fine)

Later in the program the user shall search with various criteria using text boxes, that's where it doesn't work anymore, the Query simply is not executed.

if (optBuch.Checked == true)
        {
            cmd.CommandText = 
               "SELECT Buecher.Bu_ISBN AS ISBN, 
                       Buecher.Bu_Titel AS Titel, 
                       Buecher.Bu_Originaltitel AS Originaltitel, 
                       Buecher.Bu_Buchreihe AS Buchreihe, 
                       Buecher.Bu_Genre AS Genre, 
                       Autor.Au_Vorname AS [Autor-Vorname], 
                       Autor.Au_Nachname AS [Autor-Nachname], 
                       Verlag.Ve_Name AS Verlag 
                FROM ((((Buecher 
                         INNER JOIN [Buch-Autor] 
                            ON Buecher.Bu_ID = [Buch-Autor].Bu_ID) 
                         INNER JOIN Autor 
                            ON [Buch-Autor].Au_ID = Autor.Au_ID) 
                         INNER JOIN [Buch-Verlag] 
                            ON Buecher.Bu_ID = [Buch-Verlag].Bu_ID) 
                         INNER JOIN Verlag 
                            ON [Buch-Verlag].Ve_Name = Verlag.Ve_Name)  
              WHERE (Buecher.Bu_ISBN = '%" + txtOpt1.Text + "%') 
                AND (Buecher.Bu_Titel = '%" + txtOpt2.Text + "%') 
                AND (Buecher.Bu_Originaltitel = '%" + txtOpt3.Text + "%') 
                AND (Buecher.Bu_Buchreihe = '%" + txtOpt4.Text + "%') 
                AND (Buecher.Bu_Genre = '%" + txtOpt5.Text + "%') 
                AND (Autor.Au_Vorname = '%" + txtOpt6.Text + "%') 
                AND (Autor.Au_Nachname = '%" + txtOpt7.Text + "%') 
                AND (Verlag.Ve_Name = '%" + txtOpt8.Text + "%')";

I tried various forms of the Query but until now no one worked. It works totally fine when I delete the whole " Where " section...

I hope I could express myself in a comprehensible way.

Answer 1

You cannot use the operand " = " if you want to use a wildcard. Replace " = " with "like".

So it would looks something like this:

WHERE(Buecher.Bu_ISBN like '%" + txtOpt1.Text + "%') AND
(Buecher.Bu_Titel like '%" + txtOpt2.Text + "%')

Answer 2

Beside the use of LIKE as suggested by @The Integrator you probably need OR instead of AND

Otherwise the row has to match all the criteria to be returned.

          WHERE (Buecher.Bu_ISBN = '%" + txtOpt1.Text + "%') 
            OR (Buecher.Bu_Titel = '%" + txtOpt2.Text + "%') 
            OR (Buecher.Bu_Originaltitel = '%" + txtOpt3.Text + "%') 
            OR (Buecher.Bu_Buchreihe = '%" + txtOpt4.Text + "%') 
            OR (Buecher.Bu_Genre = '%" + txtOpt5.Text + "%') 
            OR (Autor.Au_Vorname = '%" + txtOpt6.Text + "%') 
            OR (Autor.Au_Nachname = '%" + txtOpt7.Text + "%') 
            OR (Verlag.Ve_Name = '%" + txtOpt8.Text + "%')";

Also you need use parameter, otherwise you are vulnerable to Sql Injection attacks

https://stackoverflow.com/a/5165985/3470178