Field Type

Knowledge Checkpoint

This documentation assumes you are familiar with the following concepts:

• Table Type
• Origin Model

Definition

In AQL, a Field object is a part of a Table object, and it contains additional information that allows AQL to correctly transform your data. For example:

• Field origin: Dimension(orders.status)
• Field’s data type: text, number, truefalse…

In the following section, we will dive deeper into the Field Origin concept.

Field Origin

Field Origin is an important feature that allows AML to correctly query data and perform aggregations.

The field’s origin consists of three parts:

• Field class: Dimension or Measure / Metric
• The origin model: the AML model where the field was defined
• The field’s name in the AML layer

Field Origin vs. Table Origin

Unlike Table’s Origin, the Field origin is often not retained after transformation. In other words, most transformation functions when applied on fields will return a new field without the origin.

caution

Most transformation functions do not preserve the field’s origin

For example, suppose we have the following users model:

Model users {
  dimension id {}
  dimension first_name {}
  dimension last_name {}
  dimension email {}
  dimension delivered_orders {}
  dimension cancelled_orders {}
}

When writing an exploration from the users model, we create a new field called total_orders:

users 
| select(
    email,
    delivered_orders,
    cancelled_orders,
    total_orders: users.delivered_orders + users.cancelled_orders
  )

Will produce a new Table object with the following fields:

Table (origin: users)

Field	Data Type	Origin
email	Text	Dimension(users.email)
delivered_orders	Number	Dimension(users.delivered_orders)
cancelled_orders	Number	Dimension(users.cancelled_orders)
total_orders	Number	None

This new total_orders field is a new field without origin. This field can still be used in later calculations, but it will not be treated as a Dimension or Measure field, and cannot be input of some functions.

caution

Fields without origin cannot be used as Dimensions.

In other words, the following expression will be valid:

users 
| select(
    email,
    delivered_orders,
    cancelled_orders,
    total_orders: users.delivered_orders + users.cancelled_orders
  )
| select(
    email,
    cancellation_rate: cancelled_orders / total_orders
  )

And it will produce a new table:

Table (origin: users)

Field	Data Type	Origin
email	Text	Dimension(users.email)
cancellation_rate	Number	None

However, you cannot use this total_orders field as a dimension to group and then aggregate:

// Count number of users grouped by number of total orders
// However, this is an invalid expression
users 
| select(
    email,
    delivered_orders,
    cancelled_orders,
    total_orders: users.delivered_orders + users.cancelled_orders
)
| group(total_orders) // group() only accept Dimensions
| count(users.email)