Compare data from a Table in BDD with another in memory

Hi, people, The question I have is about Asp.net in c #.

First I will say that I have a code where I select an Excel file and it automatically generates a table where it puts all the data that the file contains (This with any Excel file that is placed, but I will only work with one same file and it always has the same format, the same columns, and the same fields). Up here well; Now, I have a "Users" table in my database and what I want to do with it, is to compare the "Curp" field with the other, the problem is that I do not know how to do the SQL query, or rather as I can do to compare the table I have on the page with the table in the database.

I'm still very new to Asp.Net and any help I could use would come in handy, thanks in advance.

This is the code I have to read the Excel file and the one that generates the table automatically.

    <div class="scrollver pos-grid">
        <div id="mostrar_buscar" style='display:none;'>
            Cadena a buscar <input id="searchTerm" type="text" onkeyup="doSearch()" />
        </div>
        <table id="exceltable" border="1"></table> 
    <script>
            function ExportToTable() {
                var regex = /^([a-zA-Z0-9\s_\.\-:])+(.xlsx|.xls)$/;
                /*Checks whether the file is a valid excel file*/
                if (regex.test($("#excelfile").val().toLowerCase())) {
                    var xlsxflag = false; /*Flag for checking whether excel is .xls format or .xlsx format*/
                    if ($("#excelfile").val().toLowerCase().indexOf(".xlsx") > 0) {
                        xlsxflag = true;
                    }
                    /*Checks whether the browser supports HTML5*/
                    if (typeof (FileReader) != "undefined") {
                        var reader = new FileReader();
                        reader.onload = function (e) {
                            var data = e.target.result;
                            /*Converts the excel data in to object*/
                            if (xlsxflag) {
                                var workbook = XLSX.read(data, { type: 'binary' });
                            }
                            else {
                                var workbook = XLS.read(data, { type: 'binary' });
                            }
                            /*Gets all the sheetnames of excel in to a variable*/
                            var sheet_name_list = workbook.SheetNames;

                            var cnt = 0; /*This is used for restricting the script to consider only first sheet of excel*/
                            sheet_name_list.forEach(function (y) { /*Iterate through all sheets*/
                                /*Convert the cell value to Json*/
                                if (xlsxflag) {
                                    var exceljson = XLSX.utils.sheet_to_json(workbook.Sheets[y]);
                                }
                                else {
                                    var exceljson = XLS.utils.sheet_to_row_object_array(workbook.Sheets[y]);
                                }
                                if (exceljson.length > 0 && cnt == 0) {
                                    BindTable(exceljson, '#exceltable');
                                    cnt++;
                                }
                            });
                            $('#exceltable').show();
                        }
                        if (xlsxflag) {/*If excel file is .xlsx extension than creates a Array Buffer from excel*/
                            reader.readAsArrayBuffer($("#excelfile")[0].files[0]);
                        }
                        else {
                            reader.readAsBinaryString($("#excelfile")[0].files[0]);
                        }
                    }
                    else {
                        alert("Lo sentimos, tu navegador no soporta HTML5!");
                    }
                }
                else {
                    alert("Por favor sube un archivo Excel Valido!");
                }
            }

        </script>

        <script>
            function BindTable(jsondata, tableid) {/*Function used to convert the JSON array to Html Table*/
                var columns = BindTableHeader(jsondata, tableid); /*Gets all the column headings of Excel*/
                for (var i = 0; i < jsondata.length; i++) {
                    var row$ = $('<tr/>');
                    for (var colIndex = 0; colIndex < columns.length; colIndex++) {
                        var cellValue = jsondata[i][columns[colIndex]];
                        if (cellValue == null)
                            cellValue = "";
                        row$.append($('<td/>').html(cellValue));
                    }
                    $(tableid).append(row$);
                }
            }
            function BindTableHeader(jsondata, tableid) {/*Function used to get all column names from JSON and bind the html table header*/
                var columnSet = [];
                var headerTr$ = $('<tr/>');
                for (var i = 0; i < jsondata.length; i++) {
                    var rowHash = jsondata[i];
                    for (var key in rowHash) {
                        if (rowHash.hasOwnProperty(key)) {
                            if ($.inArray(key, columnSet) == -1) {/*Adding each unique column names to a variable array*/
                                columnSet.push(key);
                                headerTr$.append($('<th/>').html(key));
                            }
                        }
                    }
                }
                $(tableid).append(headerTr$);
                return columnSet;
            }
    function doSearch() {
                var tableReg = document.getElementById('exceltable');
                var searchText = document.getElementById('searchTerm').value.toLowerCase();
                var cellsOfRow = "";
                var found = false;
                var compareWith = "";

                // Recorremos todas las filas con contenido de la tabla

                for (var i = 1; i < tableReg.rows.length; i++) {
                    cellsOfRow = tableReg.rows[i].getElementsByTagName('td');
                    found = false;
                    // Recorremos todas las celdas

                    for (var j = 0; j < cellsOfRow.length && !found; j++) {
                        compareWith = cellsOfRow[j].innerHTML.toLowerCase();
                        // Buscamos el texto en el contenido de la celda

                        if (searchText.length == 0 || (compareWith.indexOf(searchText) > -1)) {
                            found = true;
                        }
                    }
                    if (found) {
                        tableReg.rows[i].style.display = '';
                    } else {
                        // si no ha encontrado ninguna coincidencia, esconde la

                        // fila de la tabla

                        tableReg.rows[i].style.display = 'none';
                    }
                }
            }
</script>
/* Esto es para mostrar unas partes del HTML, no es importante en este caso, pero lo coloco por que va dentro del código que coloque. */
<script type="text/javascript">
            function ocultar() {
                document.getElementById('Ocultar').style.display = 'none';
            }
            function mostrar() {
                document.getElementById('Pos-Boton2').style.display = 'block';
            }
            function mostrar_buscar() {
                document.getElementById('mostrar_buscar').style.display = 'block';
            }
        </script>