AccountID    AccountName     AccountEmail
1            John Smith      john@smith.com
2            Fred John       fred@john.com
3            George Mike     george@mike.com

ItemID       ItemName        ItemDescription
1            Hammer          Smashes things
2            Axe             Breaks things

AccountItemID       AccountID     ItemID
1                   1             1
2                   2             1
3                   3             1
4                   1             2
5                   2             2

ItemName            ItemDescription    OtherOwners
Hammer              Smashes things     Fred, George
Axe                 Breaks things      Fred

AccountID    AccountName     AccountEmail       AccountDescription    AccountTypeID
1            John Smith      john@smith.com     NULL                  1
2            Fred John       fred@john.com      NULL                  1
3            George Mike     george@mike.com    Runner                2

AccountTypeID   AccountType
1               User
2               Admin

ItemName            ItemDescription    OtherOwners
Hammer              Smashes things     Fred, Runner
Axe                 Breaks things      Fred

WHERE AccountTypeID = 1 (SELECT AccountName)
WHERE AccountTypeID = 2 (SELECT AccountDescription)

SELECT
  ItemName,
  ItemDescription,
  GROUP_CONCAT(others.AccountName) as OtherOwners
FROM
  tblAccountItem as my_items
  LEFT JOIN tblAccountItem as others_items_join
    ON others_items_join.ItemID = my_items.ItemID AND others_items_join.AccountID != ?
  LEFT JOIN tblAccount as others
    ON others_items_join.AccountID = others.AccountID
  JOIN tblItems ON my_items.ItemID = tblItems.ItemID
WHERE my_items.AccountID = ?
GROUP BY ItemName

SELECT AccountName
FROM tblAccount
WHERE AccountID = (SELECT AccoundID
                   FROM tblAccountItem
                   WHERE itemID = (SELECT itemID
                                   FROM tblAccountItem
                                   WHERE AccountID = 1 (john Id as example)));