Inner Joining the same table multiple times

Question

So I have received this error: #1066 - Not unique table/alias: 'Purchase'

I am trying to do the following:

    SELECT Blank.BlankTypeCode
          ,Blank.BlankCode
          ,Payment.Amount
          ,Payment.Type
          ,Purchase.PurchaseDate
          ,Payment.DatePaid
FROM Blank
INNER JOIN Ticket
ON Blank.BlankCode = Ticket.Blank_BlankCode
INNER JOIN MCO_Blank
ON Blank.BlankCode = MCO_Blank.Blank_BlankCode
INNER JOIN Purchase
ON  Ticket.PurchaseID = Purchase.PurchaseID
INNER JOIN Purchase
ON MCO_Blank.PurchaseID = Purchase.PurchaseID
INNER JOIN Payment
ON Ticket.PurchaseID = Payment.PurchaseID
INNER JOIN Payment
ON MCO_Blank.PurchaseID = Payment.PurchaseID
WHERE Payment.Status = "Paid";

Blank Table consists of:

BlankCode,
IssueDate,
Status,
UserID, 
BlankTypeCode

Payment Table consists of:

Type,
Amount,
Status,
DueDate,
PurchaseID,
CurrencyRateDate

Purchase Table consists of:

PurchaseID,
CustomerID,
PurchaseDate,
TotalFare,
TaxAmount,
CurrencyType,
Purchasecol

Ticket Table consists of:

Price,
PurchaseID,
Blank_BlankCode,
Blank_BlankTypeCode,
TicketType,
Airline_Name

MCO_Blank Table consists of:

Service,
Cost,
Description,
Purchase_PurchaseID,
Blank_BlankCode,
Blank_BlankTypeCode

I am unsure of how I can make this work.

Answer 1

You need to use table aliases. You have mentioned the same table more than once in the from clause. The query is something like this:

SELECT b.BlankTypeCode, b.BlankCode, pa1.Amount, pa1.Type, p1.PurchaseDate, pa2.DatePaid
FROM Blank b
INNER JOIN Ticket t
ON b.BlankCode = t.Blank_BlankCode
INNER JOIN MCO_Blank mb
ON b.BlankCode = mb.Blank_BlankCode
INNER JOIN Purchase p1
ON  t.PurchaseID = p1.PurchaseID
INNER JOIN Purchase p2
ON mb.PurchaseID = p2.PurchaseID
INNER JOIN Payment pa1
ON t.PurchaseID = pa1.PurchaseID
INNER JOIN Payment pa2
ON mc.PurchaseID = pa2.PurchaseID
WHERE pa1.Status = "Paid";

I had to make a guess at which payment and purchase is intended for the aliases. These may not be correct in the from and where clauses.

Answer 2

您不能使用相同的名称多次连接表，因此要么使用inner join purchase p1 on...别名inner join purchase p1 on...或者同时使用两个连接谓词，如inner join purchase ON first predicate AND second predicate

Answer 3

You need a different alias for the table each time you use it.

SELECT B.BlankTypeCode, B.BlankCode, A1.Amount, A1.Type, P1.PurchaseDate, P1.DatePaid
  FROM Blank AS B
  JOIN Ticket    AS T  ON B.BlankCode = T.Blank_BlankCode
  JOIN MCO_Blank AS M  ON B.BlankCode = M.Blank_BlankCode
  JOIN Purchase  AS P1 ON T.PurchaseID = P1.PurchaseID
  JOIN Purchase  AS P2 ON M.PurchaseID = P2.PurchaseID
  JOIN Payment   AS A1 ON T.PurchaseID = A1.PurchaseID
  JOIN Payment   AS A2 ON M.PurchaseID = A2.PurchaseID
 WHERE A1.Status = "Paid"
   AND A2.Status = "Paid"

You'll need to sort out which versions of the Purchase and Payment tables the selected columns come from, and also what should be in the WHERE clause really.

Answer 4

SELECT bl.BlankTypeCode ,bl.BlankCode ,pymt.Amount ,pymt.Type ,purc.PurchaseDate ,pymt.DatePaid FROM Blank bl INNER JOIN Ticket tk ON bl.BlankCode = tk.Blank_BlankCode INNER JOIN MCO_Blank mco_bl ON bl.BlankCode = mco_bl.Blank_BlankCode INNER JOIN Purchase purc ON tk.PurchaseID = purc.PurchaseID AND mco_bl.PurchaseID = purc.PurchaseID INNER JOIN Payment pymt ON tk.PurchaseID = pymt.PurchaseID AND mco_bl.PurchaseID = pymt.PurchaseID WHERE pymt.Status = "Paid";

Answer 5

INNER JOIN Purchase
ON MCO_Blank.PurchaseID = Purchase.PurchaseID
INNER JOIN Payment                         --<-- 
ON Ticket.PurchaseID = Payment.PurchaseID
INNER JOIN Payment                         --<--
ON MCO_Blank.PurchaseID = Payment.PurchaseID
WHERE Payment.Status = "Paid";

You have joined Payments table twice, If you do need to join it twice you need to Alias it , a different alias everytime you join this table.