-------------------------------------- Table --------------------------------------
<table id="data-table-buttons" class="table table-striped table-bordered">
    <thead>
        <tr>
            <!--<th width="1%" data-orderable="false"></th>-->
            <th class="text-nowrap">Id</th>
            <th class="text-nowrap">Data</th>
            <th class="text-nowrap">Loja</th>
            <th class="text-nowrap">Produto</th>
            <th class="text-nowrap">Qtde</th>
            <th class="text-nowrap">Vlr. Unit.</th>
            <th class="text-nowrap">Vlr. Total</th>
        </tr>
    </thead>
</table>
-------------------------------------- Script DataTable --------------------------------------

<script type="text/javascript" language="javascript">
    $(document).ready(function() {
        $('#data-table-buttons').DataTable( {
            dom: 'Bfrtip',
            buttons: [
                'copy', 'csv', 'excel', 'pdf', 'print'
            ],
            "processing": true,
            "serverSide": true,
            "ajax": {
                "url": "busca.php",
                "type": "POST"
            },
            "columns" : [ {
                "data" : "Id"
            }, {
                "data" : "data"
            }, {
                "data" : "loja"
            }, {
                "data" : "produto"
            },{
                "data" : "qtde"
            },{
                "data" : "vlrunitario"
            },{
                "data" : "vlrtotal"
            }]
        } );
    } );
</script>

-------------------------------------- PHP --------------------------------------
Aqui eu não estou conseguindo montar pra...
RAW Paste Data
-------------------------------------- Table --------------------------------------
<table id="data-table-buttons" class="table table-striped table-bordered">
    <thead>
        <tr>
            <!--<th width="1%" data-orderable="false"></th>-->
            <th class="text-nowrap">Id</th>
            <th class="text-nowrap">Data</th>
            <th class="text-nowrap">Loja</th>
            <th class="text-nowrap">Produto</th>
            <th class="text-nowrap">Qtde</th>
            <th class="text-nowrap">Vlr. Unit.</th>
            <th class="text-nowrap">Vlr. Total</th>
        </tr>
    </thead>
</table>
-------------------------------------- Script DataTable --------------------------------------

<script type="text/javascript" language="javascript">
    $(document).ready(function() {
        $('#data-table-buttons').DataTable( {
            dom: 'Bfrtip',
            buttons: [
                'copy', 'csv', 'excel', 'pdf', 'print'
            ],
            "processing": true,
            "serverSide": true,
            "ajax": {
                "url": "busca.php",
                "type": "POST"
            },
            "columns" : [ {
                "data" : "Id"
            }, {
                "data" : "data"
            }, {
                "data" : "loja"
            }, {
                "data" : "produto"
            },{
                "data" : "qtde"
            },{
                "data" : "vlrunitario"
            },{
                "data" : "vlrtotal"
            }]
        } );
    } );
</script>

-------------------------------------- PHP --------------------------------------

<?php
include("../conexao/conexao.php");

$query = mysqli_query($conn, "select Id, data, loja, produto, qtde, vlrunitario, vlrtotal from vendas where loja=1 and data=20190102");

$result = array();
 while ($rows = mysqli_fetch_assoc($query)) {
        $id = $rows['Id'];
        $data = $rows['data'];
        $loja = $rows['loja'];
        $produto = $rows['produto'];
        $qtde = $rows['qtde'];
        $vlrunitario = $rows['vlrunitario'];
        $vlrtotal = $rows['vlrtotal'];

        $result[] = array($id,$data,$loja,$produto,$qtde,vlrunitario,$vlrtotal);
    }
}
echo json_encode(array($result));

?>