This article was previously published under Q275058
Advanced: Requires expert coding, interoperability, and multiuser skills.
This article applies only to a Microsoft Access database (.mdb).
When you run a Left Outer Join or Right Outer Join query, Microsoft Access may return incorrect data.
This behavior occurs when Access runs a SQL-92-compliant Outer Join query with a WHERE clause. Access incorrectly interprets the syntax of such a query to be an Inner Join query.
To resolve this issue, obtain the latest Microsoft Jet 4.0 service pack that contains an updated version of the Microsoft Jet 4.0 database engine.
For additional information about how to obtain the latest version of the Jet 4.0 database engine, click the following article number to view the article in the Microsoft Knowledge Base:
239114 How To: Obtain the Latest Service Pack for the Microsoft Jet 4.0 Database Engine
To work around this issue, break the query into two steps. The subquery is a Select query with the WHERE condition. It is wrapped in the main query that performs the actual left or right join operation. The following sample code is based on the procedure described in the "Steps to Reproduce the Problem" section of this article:
SELECT Employees.LastName, Employees.FirstName, Orders.OrderIDFROM Employees LEFT JOIN [SELECT * FROM Orders WHERE ShipCity = 'Warszawa']. AS Orders ON Employees.EmployeeID = Orders.EmployeeID;
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.
This problem was corrected in Jet 4.0 Service Pack 4 (SP4) and later versions.
Unlike the INNER JOIN statement, the OUTER JOIN statement returns all records from one table, even if they have no matching records in the related table. A Left Outer Join returns all rows from the table on the left side of the LEFT OUTER JOIN statement and only those records from the table on the right side of the statement that meet the relational search criteria. A Right Outer Join returns all rows from the table on the right side of the RIGHT OUTER JOIN statement and only those records from the table on the left side of the statement that meet the relational search criteria.
For example, the following query, based on the Northwind sample database, uses the SQL-92-compliant Outer Join syntax. It retrieves all employee names from the Employees table and only those OrderIDs from the Orders table where the destination city (ShipCity) is "Warszawa":
USE NorthwindGOSELECT Employees.LastName, Employees.FirstName, Orders.OrderIDFROM Employees LEFT OUTER JOIN OrdersON ((Employees.EmployeeID = Orders.EmployeeID) and (Orders.ShipCity = 'Warszawa'))
The preceding query, when run on the Microsoft SQL Server computer, correctly returns the following 11 rows:
LastName FirstName OrderID ----------------------------------- Davolio Nancy 10374 Davolio Nancy 10792 Fuller Andrew NULL Leverling Janet NULL Peacock Margaret 10906 Peacock Margaret 11044 Buchanan Steven 10870 Suyama Michael 10611 King Robert NULL Callahan Laura 10998 Dodsworth Anne NULL
Note that for the employees who never had any orders going to Warszawa, the OrderID column contains NULL. This represents the correct results according to the SQL-92 standard.
When the same query is run from Access, it returns the following seven rows
Last Name First Name Order ID ------------------------------------ Davolio Nancy 10374 Suyama Michael 10611 Davolio Nancy 10792 Buchanan Steven 10870 Peacock Margaret 10906 Callahan Laura 10998 Peacock Margaret 11044
which is equivalent to the following inner join query:
Note that all rows containing NULL in the Order ID column are missing. For the purpose of this example, Access converts the query to an Inner Join query with the same WHERE condition. As a result, only matching records are returned.
Steps to Reproduce the Problem
Start Access and open the sample database Northwind.mdb.
In the Database window, click Queries.
Double-click Create Query in Design View.
In the Show Table dialog box, click Close.
On the Query Design toolbar, click SQL, and then type or paste the following query:
SELECT Employees.LastName, Employees.FirstName, Orders.OrderIDFROM Employees LEFT OUTER JOIN OrdersON ((Employees.EmployeeID = Orders.EmployeeID) and (Orders.ShipCity = 'Warszawa'))
On the Query menu, click Run.Note that only those records with associated OrderIDs are returned. The correct results should return all employees from the Employees table, even if they have no corresponding records in the Orders table.
For more information about outer joins, visit the following Microsoft Developer Network (MSDN) Web site: