This page refers to the
from
parameter that is part of a join.
from
can also be used as part of an Explore, described on thefrom
(for Explores) parameter documentation page.
Usage
join: join_name {
from: view_name_2
}
}
Hierarchyfrom |
Default ValueA view whose name matches the join’s nameAcceptsThe name of an existing view |
Definition
from
specifies the view
to use in a join. If from
is omitted, Looker will assume that the underlying view name is the same as the join name.
Typically from
is used only if you want the join and its fields to have a different name than the underlying view. To make this clearer, consider an example where a dimension called order_value
has been created in a view called underlying_view
:
- This field would typically appear as UNDERLYING VIEW Order Value in the Explore UI and would be referenced in LookML with
${underlying_view.order_value}
. - In the usage example given above, the field would appear instead as NEW ALIAS NAME Order Value and be referenced as
${new_alias_name.order_value}
.
This technique is particularly useful when the same view needs to be joined to an Explore in several different ways.
Examples
Join the view person
to the Explore order
, but call it customer
instead:
Join the view person
to the Explore order
two different times — once as customer
and once as representative
:
Things to consider
from
changes the way fields are referenced within an Explore
As noted above, using from
has an important impact on the way that fields are referenced. This can cause some challenges when a view
is used in many different places. Consider this example:
Here person
is being joined to order
, but it is being called customer
. So, if you needed to reference a field from customer
within order
, you would use ${customer.field_name}
.
If, in a second Explore, you join person
to order
again — but don’t rename it to customer
— the ${customer.field_name}
reference will not work in that second Explore. The general approach to this issue is to exclude the problematic field from the second Explore using fields
. It would look something like this:
from
is most often used to join the same table more than once to an Explore
In cases where a single table contains different types of entities, it is possible to join a view to an Explore more than once. Suppose you had an order
Explore and needed to join a person
view to it twice — once for the customer and once for the customer service representative. You might do something like this:
The SQL that Looker would generate from this LookML is:
SELECT ...
FROM order
LEFT JOIN person AS customer
ON customer.id = order.customer_id
LEFT JOIN person AS representative
ON representative.id = order.representative_id