Group sale by days using mysql

I need to group sales by days or weeks, but I get the graph like this
view
this is the view code
function datagrafico(base_url){

plotOptions: {
column: {
pointPadding: 0.2,
borderWidth: 0
},
series:{
dataLabels:{
enabled:true,
formatter:function(){
return Highcharts.numberFormat(this.y)
}

this is the controller

and this is the models

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