Currently charts only support one string or date column which will be used for the horizontal axis or to name slices of pie charts (or similar). The other columns only can have numerical values.
This makes it difficult to plot charts if your tables are based on a Entity-attribute-value (EAV) data model. For example if you have a table with a date column, a sales amount column (value column) and column that describes the type of product you sold… you cannot plot a column chart that shows the individual sales amount per product and per year (as shown in the attachment) … you would have to pivot the table first to achieve the desired outcome.
Hence I propose a legend column that would solve this problem.