SELECT 
  cscart_banners.banner_id, 
  cscart_banners.type, 
  cscart_banners.target, 
  cscart_banners.status, 
  cscart_banners.timestamp, 
  cscart_banner_descriptions.banner, 
  cscart_banner_descriptions.description, 
  cscart_banner_descriptions.url, 
  cscart_banner_images.banner_image_id 
FROM 
  cscart_banners 
  LEFT JOIN cscart_banner_descriptions ON cscart_banner_descriptions.banner_id = cscart_banners.banner_id 
  AND cscart_banner_descriptions.lang_code = 'ru' 
  LEFT JOIN cscart_banner_images ON cscart_banner_images.banner_id = cscart_banners.banner_id 
  AND cscart_banner_images.lang_code = 'ru' 
WHERE 
  1 
  AND (
    cscart_banners.type != 'G' 
    OR cscart_banner_images.banner_image_id IS NOT NULL
  ) 
  AND cscart_banners.status = 'A' 
ORDER BY 
  cscart_banners.timestamp desc 
LIMIT 
  0, 6

Query time 0.02709

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "cscart_banners.`timestamp` desc",
            "table": {
              "table_name": "cscart_banners",
              "access_type": "ref",
              "possible_keys": ["status"],
              "key": "status",
              "key_length": "3",
              "used_key_parts": ["status"],
              "ref": ["const"],
              "rows": 3,
              "filtered": 100,
              "index_condition": "cscart_banners.`status` = 'A'",
              "attached_condition": "cscart_banners.`status` <=> 'A'"
            }
          }
        }
      },
      {
        "table": {
          "table_name": "cscart_banner_descriptions",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["banner_id", "lang_code"],
          "ref": ["cscart.cscart_banners.banner_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_banner_descriptions.lang_code = 'ru')"
        }
      },
      {
        "table": {
          "table_name": "cscart_banner_images",
          "access_type": "eq_ref",
          "possible_keys": ["banner"],
          "key": "banner",
          "key_length": "9",
          "used_key_parts": ["banner_id", "lang_code"],
          "ref": ["cscart.cscart_banners.banner_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(cscart_banners.`type` <> 'G' or cscart_banner_images.banner_image_id is not null) and trigcond(cscart_banner_images.lang_code = 'ru')"
        }
      }
    ]
  }
}