cmd.ExecuteNonQuery();
The SqlCommand instantiation is just a little different from what you've seen before, but it is basically the same. Instead of a literal string as the first parameter of the SqlCommand constructor, we are using a variable, insertString. The insertString variable is declared just above the SqlCommand declaration.
SqlCommand的实例化过程与以前看到的有一些区别，但是基本一致。在构造函数的第一个字符串参数中是用的是插入字符串变量而不三字符串字面值。该变量在SqlCommand声明之前被声明了。
Notice the two apostrophes ('') in the insertString text for the word "doesn''t". This is how you escape the apostrophe to get the string to populate column properly.
注意在insertString文本中“doesn’’t”的两个单引号（’’）。这是将它转义为适当的单引号。
Another observation to make about the insert command is that we explicitly specified the columns CategoryName and Description. The Categories table has a primary key field named CategoryID. We left this out of the list because SQL Server will add this field itself. Trying to add a value to a primary key field, such as CategoryID, will generate an exception.
