Function validateAndCreateMapping

packages/db/src/query/compiler/group-by.ts:89–121

* Validates that all non-aggregate expressions in SELECT are present in GROUP BY * and creates a cached mapping for efficient lookup during processing

(
  groupByClause: GroupBy,
  selectClause?: Select,
)

 * and creates a cached mapping for efficient lookup during processing
 */
function validateAndCreateMapping(
  groupByClause: GroupBy,
  selectClause?: Select,
): GroupBySelectMapping {
  const selectToGroupByIndex = new Map<string, number>()
  const groupByExpressions = [...groupByClause]

  if (!selectClause) {
    return { selectToGroupByIndex, groupByExpressions }
  }

  // Validate each SELECT expression
  for (const [alias, expr] of Object.entries(selectClause)) {
    if (expr.type === `agg` || containsAggregate(expr)) {
      // Aggregate expressions (plain or wrapped) are allowed and don't need to be in GROUP BY
      continue
    }

    // Non-aggregate expression must be in GROUP BY
    const groupIndex = groupByExpressions.findIndex((groupExpr) =>
      expressionsEqual(expr, groupExpr),
    )

    if (groupIndex === -1) {
      throw new NonAggregateExpressionNotInGroupByError(alias)
    }

    // Cache the mapping
    selectToGroupByIndex.set(alias, groupIndex)
  }

  return { selectToGroupByIndex, groupByExpressions }
}

/**
 * Processes the GROUP BY clause with optional HAVING and SELECT