AQLearn 2.1 / Concept

Metric Expressions

Source lesson: AQLearn 2.1: Metric Expressions. Tangible win: separate the calculation of a number (metric) from the role it plays in a report (measure or dimension).

Purpose of this lesson

Have you ever tried to answer "We need order count on the dashboard, in the cohort table, and on the customer-detail page; can we make sure they all agree"?

You hit these pain points:

Three reports re-implement the same calculation slightly differently and produce three different totals. The CEO catches it.
When the business definition changes (for example, "only delivered orders count"), you have to find and edit every copy. Some get missed.
You want the same calculation to appear sometimes as a chart number (a measure) and sometimes as a column you can group by (a dimension), but the syntax in your tool forces you to pick one.

This lesson solves it: define a calculation once as a metric expression, then plug it in wherever you need it. The same expression can power a measure or a dimension. Update the definition in one place and every report follows.

Why this matters for your mission: the metric-centric paradigm is the whole reason Holistics exists. Internalizing this distinction is what lets you defend "single source of truth" answers on presales calls.

Three words, three jobs

Metric

The named, reusable analytical value. Lives once in the dataset. Example: "order count".

Metric expression

The formula that calculates a metric. Example: orders | count(orders.id).

Measure / Dimension

The role the metric plays in a specific explore. Same expression, different slot.

Same expression, two slots

One expression. Two roles. Same number, different job in the report.

Reading the AQLearn example

metric orders_metric = orders | count(orders.id);

dimension orders.orders_metric_as_dim = orders_metric;

explore {
  measures {
    metric_as_measure: orders_metric,
  }
  dimensions {
    metric_as_dimension: orders.orders_metric_as_dim,
  }
}

metric orders_metric = ...: define the metric expression once, give it a name.
dimension orders.orders_metric_as_dim = orders_metric;: promote the same metric to a dimension on the orders model so it can be used in dimensions { }.
Inside the explore, orders_metric appears as both a measure and a dimension. Same calculation, two roles.

Side by side: definition vs use

Where	You write	You get
Dataset	`metric count_orders = orders \| count(orders.id);`	a reusable name
Explore measures	`count_orders,` or `x: orders \| count(orders.id),`	a measure slot
Model dimensions	`dimension orders.count_orders = orders \| count(orders.id);`	a dimension slot
Explore dimensions	`y: orders.count_orders,`	a dimension you can group by

Why a count can be a dimension

Once a metric is wrapped as a dimension, AQL treats its value as a label. You can:

Group customers by their order count (1 order, 2 orders, 3+).
Show each user's order count as a column next to the user, alongside other dimensions.
Filter on the value, for example "users with 3 or more orders".

Customer-safe explanation: "We define each business metric once. Reports use it as a chart number or as a grouping column without re-implementing the math."

Dataset diagram

The same AQLearn dataset. orders is the model that owns the example metric. Once orders_metric is defined on orders, every explore that joins to orders can use it.

orders grows a virtual field orders_metric_as_dim at the bottom: the same metric, attached to the model so it can be used as a dimension.

primary key foreign key

Retrieval practice

1. The formula orders | count(orders.id) is a... metric (the name) metric expression (the formula) measure (a role)

2. "Measure" and "dimension" describe... the role a field plays in a specific explore how data is stored on disk two completely different syntaxes

3. Can a single metric expression appear as both a measure in one report and a dimension in another? Yes, by attaching it to a model as a dimension and using it as a measure where needed No, you must duplicate the formula Only by writing custom SQL

4. If the business changes the definition of "order count", how many places must you update with metrics? Once, in the metric definition Every report that uses it Never; it cannot change

Do in AQLearn

Open AQLearn Metric Expressions.
Run the starter query. Confirm the same calculation appears as a measure and as a dimension column.
Add a second measure named differently but using the same metric (orders_metric) to see reuse.
Say out loud which words refer to the formula vs the role.

Next local lesson

Next: Pipe (1). How the | operator chains steps inside a metric expression.