Why do I only sometimes need substitution operators? (Community)

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Last tested: Jul 4, 2018
 

The difference is that ${foo} refers to the value in the field, whereas foo refers to the field itself. So when performing math or string operations, we'd use ${} like so:
 

dimension: do_math {

type: number

sql: ${foo} - ${bar} ;;

}

because we want the values of foo and bar to be pulled in and operated on. We do not use ${} when we are referencing the field itself, for example in drill_fields or order_by_field where we are not describing the relationship between the values, but just a relationship between the fields. So we do:

measure: sum_something {

type: sum

sql: ${something} ;;

# use ${} since we want the values to be summed

drill_fields: [foo, bar, baz]

# no ${} since we don't care about the

# values, only that these are the fields to use

}