1、使用 ' " + + " ' 拼接
string mysql = " SELECT Cname,Grade FROM student,score,course WHERE student.Sno = score.Sno and score.Cno = course.Cno and student.Sno = ‘" + Convert.ToString(textBox1.Text) + "’ and score.Text =‘" + Convert.ToInt32(comboBox1.Text) + “’; ”;
2、使用占位符
string mysql = string.Format( "SELECT Cname,Grade FROM student,score,course WHERE student.Sno = score.Sno and score.Cno = course.Cno and student.Sno = '{0}' and score.Text = '{1}' " , textbox1.Text,ComboBox1.Text);
String str="select zkzh,school,name,n1,fzf from yw01 where aaa= ' "+aaa+ " ' ";//字符串型变量
String str="select zkzh,school,name,n1,fzf from yw01 where aaa="+aaa;//int型变量