SELECT 
  dataset_id 
FROM 
  cscart_datahub_datasets 
WHERE 
  exclude_from_promotions = 1

Query time 0.00012

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.45"
    },
    "table": {
      "table_name": "cscart_datahub_datasets",
      "access_type": "ALL",
      "rows_examined_per_scan": 2,
      "rows_produced_per_join": 1,
      "filtered": "50.00",
      "cost_info": {
        "read_cost": "0.35",
        "eval_cost": "0.10",
        "prefix_cost": "0.45",
        "data_read_per_join": "2K"
      },
      "used_columns": [
        "dataset_id",
        "exclude_from_promotions"
      ],
      "attached_condition": "(`dbggbern`.`cscart_datahub_datasets`.`exclude_from_promotions` = 1)"
    }
  }
}