With effect from 2022-03-24 dashboard release:
Sub-query will enable users to introduce charts as filter values, this means that charts are run as sub-queries which will help build the data of the main chart.
What is Sub-query:
In the example below:
We have a chart called ‘Sales Overview’
This chart has been filtered using another chart called ‘Cities with Outstanding Sales’
This results in the ‘Sales Overview’ chart being filtered to only show data related to cities with outstanding sales.
This works by running the SQL query of the sub-chart, ‘Cities with Outstanding Sales’, and using the values from this chart to populate the filter for the ‘Sales Overview’ chart.
new screenshot
How does Sub-query work:
when using an in/not in operator - the first column of the data from the sub-chart is used (multiple values, as described on the tooltip in the screenshot)
top/bottom operator - sub-query charts are not allowed, so you don’t have the option to put a chart here
single value operator - the first data point (first row of the first column) is used as the value
When clicking on the drop down to pick the value for a filter, not only data can be used, charts are now also allowed to be selected as below. The type of charts allowed to be used as sub-query are similar to the merged chart/table
if a chart is allowed to be used as a sub-chart of a merged chart or table, it can be used as sub-query, this means
lines, bars, tables are allowed
pies, special shapes, maps, merged charts/tables and so on are not allowed
Reasons to use sub-query:
Sub-query mainly enables the following capabilities:
it allows sub-chart data from another data connection, e.g.
chart 1 is from a Sales data connection
chart 2 is from a HR data connection
chart 1 can have a filter, and the value is chart 2
this means you can view the sales related to employees who take a lot of holidays
it allows sub-chart data from another chart, which is built with complex sql query structure
Performance with sub-query:
Since sub-query charts are building charts to be used by other charts, the time it takes to display a chart will be the total time it takes to build all the charts used. You can see a breakdown of these times by clicking Chart Tools>Chart Information and selecting the ‘Debug’ tab - add screenshot.
To reduce the length of time taken to draw your chart, try to avoid using lots of sub-query references in your charts.
Potential problems:
Cycle referencing: If Chart 1 uses Chart 2, Chart 2 uses Chart 3, Chart 3 uses either Chart 1 or Chart 2 as sub-query, the system shows an error
Sub-charts are changed: If a sub-chart is edited afterwards, you may get unexpected results on the main chart while the main chart is not likely to be broken, because the main chart simply just picks the first column or first data point of the sub-charts, it doesn’t care how the sub-charts are configured
Sub-charts not having data: again, the main chart is not likely to display data since there isn’t anything relevant
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