Hint Values on Line Chart

Question

When you setup a line chart, the LABEL portion of the SQL query becomes the X axis value on the line chart. When there are multiple series on a line chart, each series is its own distinct line. If the series has a LABEL that is not yet on the chart, it adds that label to the x axis at the end of the axis. If the new series has a LABEL that is already on the chart, then it places the Value on that existing place on the x-axis. This Label is also used in the Hint portion of the chart.
So lets compare the number of Sales per day of a Department across a length of time, say 3 months. So, on first working day on Jan dept A has 31 sales. On the second working day of January thay make 35 sales and so on until March 31. Our company doesn't work on weekends so we won't have sales on those dates. Dept B has their numbers for the same dates.
We setup a series for each month (Jan, Feb, March). Then we place the total number of orders for each date on the graph and connect the dots! Great! But wait, the more months I add, the shorter each line gets on the graph. What if we were comparing 3 years worth of data instead of 3 months. The x-axis would have 600-700 values instead of 60-70 values. Oh my.
What if we make each series of data its own line over the same scale? That way each month shows in the same space with the first day of the month at the left and the last day of the month near the right. Sounds good. But wait, we are now making up a scale. And when we do this, the Hints on the data points become meaningless. I want to show the actual date value in the hint but have the line over my custom X-Axis. What I need is an additional field that I can use to add to the Hint portion of the chart. Obviously, this would require using custom xml and a custom data element, but is this even possible given the constraints of the SQL syntax?
To visualize this issue better: http://apex.oracle.com/pls/otn/f?p=28155:1
Austin

Answer 1

Andy -
I need to thank you for the direction on the substitution variables reference. That will be a major help.
However, i must correct a statement (underlining is mine)
So, if you switch to Custom XML and find the <tooltip> tag and add {%SeriesName} after the existing {%Name} entry, you end up with the _"day of the month" (which is your value)_ and the Series Name value, which is January - so, "1 January"This is a common misconception that the numeric value on the x axis represent the "day of the month" , when in fact it does not. You logically cannot use the day of the month for this type of axis. Why not? It is because weekends are excluded. So, one month may begin on a Friday. If that were the case then the 2nd of the month would be a Saturday, which would work for a single series of data. But what about when you add in the next month and it begins on a Tuesday. Well then, if you use the day of the month as the value, the 2nd day of the second series actually gets plotted after all the days of the first month.
The solution is that you have to generate a common arbitrary scale for all series of data. When you do that, you lose the date values.
I have tried to illustrate all of this by adding to the existing examples in the link provided above. Some other odd behaviors of using the day of the month as the x-axis value can be seen as well. I have also implemented the suggestion of adding the {%SeriesName} tag to the Hint via the custom xml.
Austin