SELECT 
  linked_promotion_id 
FROM 
  cscart_product_bundles

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_bundles",
      "access_type": "system",
      "rows": 0,
      "filtered": 0,
      "const_row_not_found": true
    }
  }
}