SELECT 
  cscart_attachments.*, 
  cscart_attachment_descriptions.description 
FROM 
  cscart_attachments 
  LEFT JOIN cscart_attachment_descriptions ON cscart_attachments.attachment_id = cscart_attachment_descriptions.attachment_id 
  AND lang_code = 'en' 
WHERE 
  object_type = 'product' 
  AND object_id = 339747 
  AND type = 'M' 
  AND (
    usergroup_ids = '' 
    OR FIND_IN_SET(0, usergroup_ids) 
    OR FIND_IN_SET(1, usergroup_ids)
  ) 
  AND status = 'A' 
ORDER BY 
  position

Query time 0.00079

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.32"
    },
    "ordering_operation": {
      "using_filesort": true,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_attachments",
            "access_type": "ref",
            "possible_keys": [
              "object_type",
              "type"
            ],
            "key": "object_type",
            "used_key_parts": [
              "object_type",
              "object_id"
            ],
            "key_length": "95",
            "ref": [
              "const",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "10.00",
            "index_condition": "((`webmarco`.`cscart_attachments`.`object_type` <=> 'product') and (`webmarco`.`cscart_attachments`.`object_id` <=> 339747))",
            "cost_info": {
              "read_cost": "1.00",
              "eval_cost": "0.02",
              "prefix_cost": "1.20",
              "data_read_per_join": "195"
            },
            "used_columns": [
              "attachment_id",
              "object_type",
              "object_id",
              "type",
              "position",
              "filename",
              "filesize",
              "usergroup_ids",
              "status",
              "url",
              "on_server"
            ],
            "attached_condition": "((`webmarco`.`cscart_attachments`.`type` = 'M') and ((`webmarco`.`cscart_attachments`.`usergroup_ids` = '') or find_in_set(0,`webmarco`.`cscart_attachments`.`usergroup_ids`) or find_in_set(1,`webmarco`.`cscart_attachments`.`usergroup_ids`)) and (`webmarco`.`cscart_attachments`.`status` = 'A'))"
          }
        },
        {
          "table": {
            "table_name": "cscart_attachment_descriptions",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "attachment_id",
              "lang_code"
            ],
            "key_length": "9",
            "ref": [
              "webmarco.cscart_attachments.attachment_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.10",
              "eval_cost": "0.02",
              "prefix_cost": "1.32",
              "data_read_per_join": "78"
            },
            "used_columns": [
              "attachment_id",
              "lang_code",
              "description"
            ]
          }
        }
      ]
    }
  }
}