SELECT 
  company_id 
FROM 
  cscart_companies

Query time 0.00029

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "3.47"
    },
    "table": {
      "table_name": "cscart_companies",
      "access_type": "index",
      "key": "PRIMARY",
      "used_key_parts": [
        "company_id"
      ],
      "key_length": "4",
      "rows_examined_per_scan": 6,
      "rows_produced_per_join": 6,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "2.27",
        "eval_cost": "1.20",
        "prefix_cost": "3.47",
        "data_read_per_join": "42K"
      },
      "used_columns": [
        "company_id"
      ]
    }
  }
}