indexEqualityScan method

CostEstimate indexEqualityScan(String table, String column, dynamic value)

Implementation

CostEstimate indexEqualityScan(
    String table, String column, dynamic value) {
  final ts = stats.get(table);
  if (ts == null) {
    return const CostEstimate(
        totalCost: 10.0, rows: 1.0, method: 'IndexScan(unknown)');
  }
  final cs = ts.column(column);
  final rowCountSafe = ts.rowCount < 1 ? 1 : ts.rowCount;
  final sel = cs?.equalitySelectivity() ?? (1.0 / rowCountSafe);
  final maxRows = rowCountSafe.toDouble();
  final matchRows = (rowCountSafe * sel).clamp(1.0, maxRows);

  final cost = CostConstants.indexFetchCost +
      matchRows * (CostConstants.randomIoCost + CostConstants.cpuTupleCost);
  return CostEstimate(
      totalCost: cost,
      rows: matchRows,
      method: 'IndexScan($table.$column=$value)');
}