I don't know of any better way to ask this question.

If the below code is run (i know the cData sections are not visible in the preview, something causes it to be ignored).

The result does not represent the data correctly. 1. Flex ignores missing date 24 aug for DECKER. 2. It wrongly associates 42.77 to 23-Aug instead of 24-AUG.

Is there a way in flex, where the x-axis is a union of all available points ?

The below code is entirely from : Adobe website link

I have only commented 2 data points. //{date:"23-Aug-05", close:45.74}, and //{date:"24-Aug-05", close:150.71},

<?xml version="1.0"?>

 [Bindable]
  public var SMITH:ArrayCollection = new ArrayCollection([
    {date:"22-Aug-05", close:41.87},
    //{date:"23-Aug-05", close:45.74},
    {date:"24-Aug-05", close:42.77},
    {date:"25-Aug-05", close:48.06},
 ]);

 [Bindable]
  public var DECKER:ArrayCollection = new ArrayCollection([
    {date:"22-Aug-05", close:157.59},
    {date:"23-Aug-05", close:160.3},
    //{date:"24-Aug-05", close:150.71},
    {date:"25-Aug-05", close:156.88},
 ]);

[Bindable]
public var deckerColor:Number = 0x224488;

[Bindable]
public var smithColor:Number = 0x884422;

]]>

    <mx:horizontalAxisRenderers>
        <mx:AxisRenderer placement="bottom" axis="{h1}"/>
    </mx:horizontalAxisRenderers>

    <mx:verticalAxisRenderers>
        <mx:AxisRenderer placement="left" axis="{v1}">
            <mx:axisStroke>{h1Stroke}</mx:axisStroke>
        </mx:AxisRenderer>
        <mx:AxisRenderer placement="left" axis="{v2}">
            <mx:axisStroke>{h2Stroke}</mx:axisStroke>
        </mx:AxisRenderer>
    </mx:verticalAxisRenderers>

    <mx:series>
       <mx:ColumnSeries id="cs1" 
            horizontalAxis="{h1}" 
            dataProvider="{SMITH}" 
            yField="close" 
            displayName="SMITH"
        >
            <mx:fill>
                <mx:SolidColor color="{smithColor}"/>
            </mx:fill>

            <mx:verticalAxis>
               <mx:LinearAxis id="v1" minimum="40" maximum="50"/>
            </mx:verticalAxis>           
       </mx:ColumnSeries>           
       <mx:LineSeries id="cs2" 
            horizontalAxis="{h1}" 
            dataProvider="{DECKER}" 
            yField="close" 
            displayName="DECKER"
        >
            <mx:verticalAxis>
                <mx:LinearAxis id="v2" minimum="150" maximum="170"/>           
            </mx:verticalAxis>

            <mx:lineStroke>
                <mx:Stroke 
                    color="{deckerColor}" 
                    weight="4" 
                    alpha="1"
                />
            </mx:lineStroke>
       </mx:LineSeries>
    </mx:series>
 </mx:ColumnChart>
 <mx:Legend dataProvider="{myChart}"/>