Cross Join is also called Cartesian Join. It's named after the great French philosopher and mathematician René Descartes. The original spelling of his family name is in two words: Des Cartes, therefore Cartesian. Among many great inventions, he is well known for saying: I think therefore I am (Je pense donc je suis).
Cross Join is quite useful in data manipulation in creating Sigmoid/Spline based charts (Sankey for example), data scaffolding and many other applications.

Some may wonder why Tableau doesn't offer Cross Join within its join interface. I guess that it's because there are so many ways we can do it already. Here let me summarize them here.

1.Via Custom SQL with Union
Assume we want to cross join two tables: A and B. This works when one of the 2 tables is smaller with just a few rows (and a few columns). Assume here B has only 2 rows and 1 column:
Let's open Table A (Orders table in Superstore data set) in Excel file via Legacy Connection. This gives us the option to write Custom SQL.
This creates the cross join between the two tables! This is an application in creating Sigmoid curve.

If B has more rows, we just need to add more such unions. If B has more columns, we need to explicitly spell them out for each and every element of the columns in the query.

As we mentioned before, this approach is good if B is small.

2.Via Custom SQL with Excel
Once I needed to create a table structure via cross join for scaffolding. Then I put the tables into separate sheets in one Excel file. Opening it via legacy connection and using Custom SQL, I am able to cross join them easily.


This approach is fairly universal and only needs a single line of SQL code.

3.Via Tableau's Native Inner Join Dialog
Zen Master Jeffrey Shaffer described this cross join approach early on. Kettan wrote a great tutorial by creating an extra identical Join Key column in each joining table. The Join Key column can be populated with the same number such as 1 or the same string such as 'Join'.
4.Via Tableau Join Calculation (Tableau 10.2+) (See updates in comments)
This approach doesn't need SQL nor pre-populated Join Key column. No need to reshape data. This can work across different data sources. It's the most versatile approach.

In Tableau 10.2+, we can use "Join Calculation" to create Join Keys in both joining tables. Here we created '1' column in both tables. Note that only the first Join Key can be 1, while the other has to be generated using a formula. The dialog just doesn't let me to enter 1 in both Join Calculations. No need of pre-populated Join Key any more.
I was told by Zen Master Chris Love that Bethany Lyons of Tableau demoed something similar at Tableau Conference 2016. After viewing the video, I found that she used Join Calculation in one table, and pre-populated the other table with a Join Key column. It works as well.

Voila, a little review of the four approaches for Cross Join in Tableau. Pick the one that's appropriate for you. Let me know if you have different approaches.

This is a sequel to my recent post: #TweakThursday 22: Ordering By Narrative. That one is focusing on dashboard tweaking. Here I would give details on ways of boosting a stacked area chart.

Stacked area chart is visually attractive in displaying multiple members' values evolving along another dimension, such as time series.

There may be various ways of coloring the stacked area chart. But I found that using gradient shades of the same color makes the chart highly attractive.

On the other hand, stacked area chart is vertically challenged because we can't compare easily along the vertical dimension. The contrast is not as sharp as in bar chart. We will add a bar chart in tooltips to boost the vertical comparison.

The example here is based on a viz by Andy Cotgreave and a recent Viz of the Day, results of the #MakeoverMonday.

1. Coloring the chart
The main steps include:
- Using gradient (discrete) shades of the same color
- Darker to lighter from bottom to top
- Highlighting one member using a different color if needed

Please refer to this article on highlighting one member among others in gradient shades of the same color. The highlighting can be made dynamic via a parameter.

2. Tooltip design
In the bar chart in tooltips, I would like to highlight the data mark I am hovering opon in a different color. I thus need 3 sets of new fields/variables. For a given dimension member, only one of the blue bar and the orange bar is lighted up at anytime.

The creation of the following variables can be made easier by a technique here. The bar chart in tooltips is described here.

- Blue bars for the data marks when they are not hovered upon. Note that a window function has to be used to get the values of non-hovered data marks.
- Orange bars for the data marks when they are hovered upon.
The code for the tooltips are as follows:
The resulting tooltip is as follows:

That's how we can make a boosted stacked area chart. This technique can apply to stacked bar chart or any chart where you want to enhance the contrast in some dimension.

The workbook can be accessed here to view the tooltips in action.