Function getAggregateFunction

packages/db/src/query/compiler/group-by.ts:517–569

* Helper function to get an aggregate function based on the Agg expression

(aggExpr: Aggregate)

 * Helper function to get an aggregate function based on the Agg expression
 */
function getAggregateFunction(aggExpr: Aggregate) {
  // Pre-compile the value extractor expression
  const compiledExpr = compileExpression(aggExpr.args[0]!)

  // Create a value extractor function for the expression to aggregate
  const valueExtractor = ([, namespacedRow]: [string, NamespacedRow]) => {
    const value = compiledExpr(namespacedRow)
    // Ensure we return a number for numeric aggregate functions
    if (typeof value === `number`) {
      return value
    }
    return value != null ? Number(value) : 0
  }

  // Create a value extractor function for min/max that preserves comparable types
  const valueExtractorForMinMax = ([, namespacedRow]: [
    string,
    NamespacedRow,
  ]) => {
    const value = compiledExpr(namespacedRow)
    // Preserve strings, numbers, Dates, and bigints for comparison
    if (
      typeof value === `number` ||
      typeof value === `string` ||
      typeof value === `bigint` ||
      value instanceof Date
    ) {
      return value
    }
    return value != null ? Number(value) : 0
  }

  // Create a raw value extractor function for the expression to aggregate
  const rawValueExtractor = ([, namespacedRow]: [string, NamespacedRow]) => {
    return compiledExpr(namespacedRow)
  }

  // Return the appropriate aggregate function
  switch (aggExpr.name.toLowerCase()) {
    case `sum`:
      return sum(valueExtractor)
    case `count`:
      return count(rawValueExtractor)
    case `avg`:
      return avg(valueExtractor)
    case `min`:
      return min(valueExtractorForMinMax)
    case `max`:
      return max(valueExtractorForMinMax)
    default:
      throw new UnsupportedAggregateFunctionError(aggExpr.name)
  }
}

/**
 * Transforms expressions to replace aggregate functions with references to computed values.