SELECT 
  c.company_id, 
  c.sd_ga_tracking_code 
FROM 
  cscart_companies as c 
  LEFT JOIN cscart_vendor_plans as v ON c.plan_id = v.plan_id 
WHERE 
  v.ga_vendors_tracking = 'Y'

Query time 0.00010

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "v",
      "access_type": "ALL",
      "possible_keys": ["PRIMARY"],
      "rows": 5,
      "filtered": 100,
      "attached_condition": "v.ga_vendors_tracking = 'Y'"
    },
    "block-nl-join": {
      "table": {
        "table_name": "c",
        "access_type": "ALL",
        "rows": 11,
        "filtered": 100
      },
      "buffer_type": "flat",
      "buffer_size": "97",
      "join_type": "BNL",
      "attached_condition": "c.plan_id = v.plan_id"
    }
  }
}