Instructions

1. Syntax:
   • {{ value }}: Output syntax (inserts text).
   • {% if condition %}: Tag syntax (logic).
2. Common Variables:
   • value: Raw value from DB (best for comparisons).
   • rendered_value: Formatted value (best for display).
   • _filters['view.field']: User-selected filter values.
   • parameter_name._parameter_value: Selected parameter value.
3. Best Practices:
   • SQL Injection: Always use | sql_quote when inserting user input (like _filters) into SQL that generates string literals.
   • Booleans: If your dialect requires literal TRUE/FALSE (like BigQuery), append | sql_boolean to _in_query or _is_selected variables (e.g., {{ view.field._in_query | sql_boolean }}).
   • Dependency Awareness: Remember that _in_query checks for usage in SELECT, Filters, and required_fields. It is NOT limited to just the visible columns.
   • Performance: Avoid referencing {{ field._value }} in link parameters if the field isn't already in the query, as this forces Looker to add the field to the GROUP BY clause, potentially fan-outing the result set. Use row['view.field'] instead if you only need the value from the browser result row.

Advanced Variable Usage

_in_query vs _is_selected