[Solved]-Overlapping columns in highchart-Highcharts

edit highcharts has introduced plotoptions.column.grouping switch in their version 2.3 to handle exactly this. refer garrick's answer

i will leave below answer as it still helps understand how the grouppadding and pointwidth work.

original answer

you are looking for grouped and overlapping columns?

you can achieve this by setting plotoptions.column.grouppadding to 0.5

plotoptions: {
    column: {           
        grouppadding: 0.5   // exactly overlap
        pointwidth: 20,                                     
    }
},

here's an image to illustrate how grouppadding works

as you see, when grouppadding is 0.5 the column width is compromised to give the desired padding, by specifying the pointwidth you can counter this behavior