c# - sql中不能减

Question

 string sql2 = "UPDATE project_table 
                SET resources=(resources-" + txtresource.Text + ") 
                where code=" + project_code + "";

我使用下面的查询来更新我的表，但我的数据库似乎没有减少资源。我做错了什么？

Answer 1

转换它，然后在查询中使用，例如

int val = Convert.ToInt32(txtresource.Text.Trim());
SET resources = resources - val

最后考虑使用SQLParameter来避免SQL注入(inject)攻击

string sql2 = "UPDATE project_table SET resources = resources - @val where code = @code";
//Create Command
SqlCommand cmd = new SqlCommand(sql2, connectionObject);
cmd.CommandType = CommandType.Text;

cmd.Parameters.Add(SQLDbType.INT, @val).Value = val;
cmd.Parameters.Add(SQLDbType.VARCHAR, @code).Value = project_code;