Querying relationships
This section will explain how we can query relationships by using the JOIN operator. The JOIN operator allows us to join (or combine, as we say) different result sets of digital twins. You can add up to five JOIN operators in one query.
There are some rules that we have to apply when using a JOIN operator. These rules are as follows:
- We need to specify a name for a result set. That means that we need to replace
FROM DIGITALTWINSwith, for example,FROM DIGITALTWINS DT.DT, is, in this case, the name of the result set. The name can be anything we want. - The query is required to have a
$dtIdvalue in theWHEREclause. - The
SELECT *needs to be replaced with, for example,SELECT DT, RT.DTandRT, in this case, are both result sets. At least one result set or a specific field in a result set is required.
The following query does a JOIN operation between digital twins with a specified relationship called contains. In our current Azure Digital...