在 JDBC 中连接三个表

Question

我有这段代码并且不断收到语法错误。

query = "SELECT * "+
"FROM Product " +
"INNER JOIN Orders ON (Product.ItemID=Orders.ItemID) " +
"LEFT OUTER JOIN SupplierProduct ON (Orders.ItemID=SupplierProduct.ItemID) "+
"WHERE Product.Receiver = 'Fred' " +
"ORDER BY Product.ItemName";    

DefaultTableModel data = table.getQuery(query);

我也试过用INNER JOIN 代替LEFT OUTER JOIN。我一直在尝试的错误是。

java.sql.SQLException: [Microsoft][ODBC Microsoft Access Driver] Syntax error (missing     operator) in query expression '(Product.ItemID=Orders.ItemID) LEFT OUTER JOIN  SupplierProduct ON (Orders.ItemID=SupplierProduct.ItemID'.
at sun.jdbc.odbc.JdbcOdbc.createSQLException(Unknown Source)
at sun.jdbc.odbc.JdbcOdbc.standardError(Unknown Source)
at sun.jdbc.odbc.JdbcOdbc.SQLExecDirect(Unknown Source)
at sun.jdbc.odbc.JdbcOdbcStatement.execute(Unknown Source)

我在这里缺少什么或如何加入三个表。

Answer 1

尝试像这样使用括号：

query = "SELECT * "+
        "FROM (Product " +
        "INNER JOIN Orders ON (Product.ItemID=Orders.ItemID)) " +
        "LEFT OUTER JOIN SupplierProduct ON (Orders.ItemID=SupplierProduct.ItemID) "+
        "WHERE Product.Reciever = 'Fred' " +
        "ORDER BY Product.ItemName";  

Answer 2

看起来 JDBC 可能难以解析连接的顺序。这可能是您正在与之交互的数据库引擎特有的问题，但无论如何，如果您使用括号指定连接操作的顺序，任何引擎都应该能够正确解析查询：

query = "SELECT * "+
"FROM (Product " +
"INNER JOIN Orders ON (Product.ItemID=Orders.ItemID)) " +
"LEFT OUTER JOIN SupplierProduct ON (Orders.ItemID=SupplierProduct.ItemID) "+
"WHERE Product.Reciever = 'Fred' " +
"ORDER BY Product.ItemName";    

DefaultTableModel data = table.getQuery(query);

更多细节：

基本上，这个想法是分离每个连接，以便它可以或多或少地被解释为一个独立的表。这有助于更完全地区分

SELECT * 
FROM (Table1 JOIN Table2 ON Table1.a = Table2.a) 
     JOIN Table3 on Table3.b = Table2.b

来自

SELECT * 
FROM Table1 
     JOIN (Table2 JOIN Table3 on Table3.b = Table2.b) ON Table1.a = Table2.a

另外，请注意，您可能需要为第一次连接的结果设置别名，如下所示：

SELECT * 
FROM (Table1 JOIN Table2 ON Table1.a = Table2.a) as join1 
     JOIN Table3 on Table3.b = join1.b