SELECT 
  * 
FROM 
  cscart_usergroup_descriptions 
WHERE 
  usergroup_id = 1 
  AND (
    usergroup = 'rep group' 
    OR usergroup = 'rep group'
  )

Query time 0.00047

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_usergroup_descriptions",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["usergroup_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_usergroup_descriptions.usergroup = 'rep group' or cscart_usergroup_descriptions.usergroup = 'rep group'"
    }
  }
}