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Lookup Expressions

Indicate dimension fields with lookup expressions.

Overview​

Lookup expressions are optional indicators that a dimension field is a lookup/dimension field. They help the planner understand field semantics.

Basic Syntax​

expression:
  lookup: true
  sql: column_name

When to Use​

Lookup expressions are optional but can help with:

  • Query planning optimization
  • Field semantics documentation
  • Planner understanding of field types

Example​

- type: dimension
  name: Product Category
  data_type: string
  expression:
    lookup: true
    sql: category_name

Notes​

  • Optional - SQL expressions work without lookup: true
  • Dimensions only - Not used for measures
  • Semantic indicator - Helps planner understand field purpose

Complete Example​

fields:
  - type: dimension
    name: Customer Name
    data_type: string
    expression:
      lookup: true
      sql: customer_name

  - type: dimension
    name: Product Category
    data_type: string
    expression:
      lookup: true
      sql: category_name

  - type: measure
    name: Total Revenue
    data_type: decimal
    expression:
      sql: sum(amount)  # No lookup for measures

Best Practices​

  1. Use for clarity - Makes field semantics explicit
  2. Optional - Not required, but can help documentation
  3. Dimensions only - Don't use for measures

Next Steps​