lookml-fields

name	lookml-fields
description	Overview of LookML field types (Dimension, Measure, Filter, Parameter) and the role of the `sql` parameter in each. Use this skill to choose the right field type for your data modeling needs.

Instructions

1. Field Types Overview

LookML fields are the building blocks of your data model. Each type serves a specific purpose in generating SQL.

Field Type	Purpose	SQL Generation Phase
Dimension	Describes data (attributes). Groups results.	SELECT and GROUP BY clause.
Measure	Aggregates data (metrics). Calculates results.	SELECT clause (with aggregation).
Filter	Restricts data based on conditions.	WHERE or HAVING clause (via templated filters).
Parameter	Captures user input for dynamic logic.	None directly (injects values into other fields).
Dimension Group	Generates a set of time-based dimensions.	SELECT and GROUP BY clause (multiple columns).

2. The Role of sql Parameter

The sql parameter behaves differently strictly based on the field type.

Dimensions: The "What"

• Role: Defines the raw transformation of the column before any aggregation.
• SQL Context: The expression is placed directly into the GROUP BY clause.
• Input: Can reference table columns (${TABLE}.col), other dimensions (${dim}), or raw SQL functions.
• Example:

  dimension: full_name {
    sql: CONCAT(${first_name}, ' ', ${last_name}) ;;
  }
  -- Generates: CONCAT(table.first_name, ' ', table.last_name)
  

Measures: The "How Much"

• Role: Defines the value to be aggregated or the calculation involving other aggregates.
• SQL Context: Puts the expression inside the aggregation function (e.g., SUM(sql)), or as a standalone calculation for type: number.
• Input:
  • For type: sum/avg/min/max: References dimensions or columns.
  • For type: number: References other measures.
  • For type: count: sql is ignored (always COUNT(*) or COUNT(primary_key)).
• Example:

  measure: total_profit {
    type: sum
    sql: ${sale_price} - ${cost} ;; 
  }
  -- Generates: SUM(sale_price - cost)
  

Filters: The "Which"

• Role: Defines the condition logic, usually for Templated Filters used in Derived Tables or sql_always_where.
• SQL Context: The sql parameter in a filter field is rarely used directly in modern LookML. Instead, the input to the filter is used in {% condition %} tags.
• Best Practice: Identify if you need a filter field or just a parameter + dimension.
• Example (Templated Filter):

  filter: date_filter { type: date }
  -- Usage in Derived Table SQL:
  -- WHERE {% condition date_filter %} created_at {% endcondition %}
  

Parameters: The "User Input"

• Role: Does NOT generate SQL itself. It holds a user-selected value to be injected into other fields.
• SQL Context: Accessed via Liquid variables ({% parameter name %}) inside Dimensions, Measures, or Derived Tables.
• Input: User selects from a UI list or types a value.
• Example:

  parameter: timeframe_selector {
    type: unquoted
    allowed_value: { value: "month" }
    allowed_value: { value: "year" }
  }
  dimension: dynamic_date {
    sql: DATE_TRUNC({% parameter timeframe_selector %}, ${created_raw}) ;;
  }
  

Dimension Groups: The "Time Generator"

• Role: Defines the source timestamp or date column. Looker then generates multiple dimension fields based on the timeframes list.
• SQL Context: Casts and truncates the source column for each timeframe.
• Input: Must be a standardized timestamp or date expression.
• Example:

  dimension_group: created {
    type: time
    timeframes: [date, month]
    sql: ${TABLE}.created_at ;;
  }
  -- Generates:
  -- created_date -> CAST(table.created_at AS DATE)
  -- created_month -> DATE_TRUNC(table.created_at, MONTH)
  

3. Summary of Differences

Type	sql references...	Can reference Measures?	Aggregated?
Dimension	Columns, Other Dimensions	NO	No
Measure (Agg)	Columns, Dimensions	NO	Yes
Measure (Num)	Other Measures	YES	Yes (already agg)
Filter	(Rarely used)	No	N/A
Parameter	(None)	No	N/A
Value Format	(None)	No	N/A

Reference Skills

For detailed standards on specific field types, refer to:

• Dimensions: Naming, labels, and type-specific rules.
• Measures: Aggregation types, filters, and formats.
• Filters & Parameters: Templated filters and user input.
• Dimension Groups: Timeframes and intervals.
• Value Formats: Named and custom currency/number formats.