C#查询数据库提示列名无效是什么意思

代码为
string sql=string.format("update teacher set sex={0} where teachername={1}",sex,cb.text);
sqlcommand command=new sqlcommand(sql,connection);
int result=0;
result=command.executenonquery（）;
列名没错误，请问是什么问题呢

能把string sql=string.format("update teacher set sex={0} where teachername={1}",sex,cb.text);的执行结果 sql字符串的内容贴出来吗??,用参数查询我们一般不用format,format只是简单处理格式,{0}和替换成sex的值,但不会给你加上 ' '号,sql语句可能就错了,带参数的sql查询,一般用SqlParameter这个对象,你查查,给你个例子,
SqlParameter[] mysqlpara1 = new SqlParameter[2];
SqlParameter[] mysqlpara2 = new SqlParameter[3];

mysqlpara1[0] = new SqlParameter("@userid",SqlDbType.NChar,10);
mysqlpara1[0].Value = txtUserID.Text;

mysqlpara1[1] = new SqlParameter("@passwd",SqlDbType.NChar,10);
mysqlpara1[1].Value = txtPassWord.Text;

strSql=@"select count(*) from userauth where userid=@userid and passwd=@passwd";