SQL server table data into JSON (C# code)

if you asp.net with c# behindcode you can use sqldatasource on aspx and on codebehind write this code:

protected void Page_Load(object sender, EventArgs e)
        {
            DataView dv = (DataView)SqlDataSource1.Select(DataSourceSelectArguments.Empty);
            DataTable dt = dv.ToTable();
            System.Web.Script.Serialization.JavaScriptSerializer serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
            List<dictionary><string,>> rows = new List<dictionary><string,>>();
            Dictionary<string,> row;
            foreach (DataRow dr in dt.Rows)
            {
                row = new Dictionary<string,>();
                foreach (DataColumn col in dt.Columns)
                {
                    row.Add(col.ColumnName, dr[col]);
                }
                rows.Add(row);
            }
                string data = serializer.Serialize(rows);
                string script= String.Format("<script type=\"text/javascript\">var jsondata = {0}</script>",data);
                if (!this.ClientScript.IsClientScriptBlockRegistered("datascript"))
                {
                    this.ClientScript.RegisterClientScriptBlock(this.GetType(), "datascript", script);
                }
            }
        }

Don't forget to add register script block on aspx page.

JSON serializer is only good if you both write and read the data. All serializers allow you to store some object graph to a stream and later restore if from stream. Roughly speaking, if you stored JSON once, you can figure out its structure and write JSON manually, following this structure, or write code using different system, not using Data Contract (for example, because this is not .NET).

But if JSON is given, you need to follow its structure. The approach when you mirror your database schema also may not work, because that given JSON wasn't designed for your database. Then you can design some .NET type to follow the given JSON. I explained it in my past answers:
How To Convert object type to C# class object type[^],
pass json data to javascript?[^].

I must say, you did not provide enough information and didn't answer my question, so the answers are based on too much of guesswork.

—SA