SELECT 
  tax_ids 
FROM 
  cscart_shippings 
WHERE 
  shipping_id = 37

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_shippings",
      "access_type": "const",
      "possible_keys": ["shipping_id"],
      "key": "shipping_id",
      "key_length": "3",
      "used_key_parts": ["shipping_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    }
  }
}