Could not use the same linked table multiple times in the same query.

h2/src/docsrc/html/changelog.html

@@ -18,7 +18,8 @@ Change Log
 <h1>Change Log</h1>
 
 <h2>Next Version (unreleased)</h2>
-<ul><li>A bug in the server-less multi-connection mode has been fixed.
+<ul><li>Could not use the same linked table multiple times in the same query.
+</li><li>A bug in the server-less multi-connection mode has been fixed.
 </li><li>Column names could not be named "UNIQUE" (with the quotes).
 </li><li>New system function TRANSACTION_ID() to get the current transaction
     identifier for a session.

h2/src/docsrc/html/roadmap.html

@@ -407,6 +407,7 @@ Of course, patches are always welcome, but are not always applied as is. Patches
 </li><li>PostgreSQL compatibility: test DbVisualizer and Squirrel SQL using a new PostgreSQL JDBC driver.
 </li><li>RunScript should be able to read from system in (or quite mode for Shell).
 </li><li>Natural join: support select x from dual natural join dual.
+</li><li>Optimize IN(...) for DELETE and UPDATE.
 </li></ul>
 
 <h2>Not Planned</h2>

h2/src/main/org/h2/index/LinkedCursor.java

@@ -6,6 +6,7 @@
  */
 package org.h2.index;
 
+import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 
@@ -14,7 +15,7 @@ import org.h2.message.Message;
 import org.h2.result.Row;
 import org.h2.result.SearchRow;
 import org.h2.table.Column;
-import org.h2.table.Table;
+import org.h2.table.TableLink;
 import org.h2.value.DataType;
 import org.h2.value.Value;
 
@@ -23,15 +24,24 @@ import org.h2.value.Value;
  */
 public class LinkedCursor implements Cursor {
 
-    private Session session;
+    private final TableLink tableLink;
+    private final PreparedStatement prep;
+    private final String sql;
+    private final Session session;
+    private final ResultSet rs;
     private Row current;
-    private ResultSet rs;
-    private Table table;
 
-    LinkedCursor(Table table, ResultSet rs, Session session) {
+    LinkedCursor(TableLink tableLink, ResultSet rs, Session session, String sql, PreparedStatement prep) {
         this.session = session;
-        this.table = table;
+        this.tableLink = tableLink;
         this.rs = rs;
+        this.sql = sql;
+        this.prep = prep;
+    }
+
+    private void closeResultSetAndReusePreparedStatement() throws SQLException {
+        rs.close();
+        tableLink.reusePreparedStatement(prep, sql);
     }
 
     public Row get() {
@@ -50,13 +60,13 @@ public class LinkedCursor implements Cursor {
     public boolean next() throws SQLException {
         boolean result = rs.next();
         if (!result) {
-            rs.close();
+            closeResultSetAndReusePreparedStatement();
             current = null;
             return false;
         }
-        current = table.getTemplateRow();
+        current = tableLink.getTemplateRow();
         for (int i = 0; i < current.getColumnCount(); i++) {
-            Column col = table.getColumn(i);
+            Column col = tableLink.getColumn(i);
             Value v = DataType.readValue(session, rs, i + 1, col.getType());
             current.setValue(i, v);
         }

h2/src/main/org/h2/index/LinkedIndex.java

@@ -10,7 +10,6 @@ import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 
-import org.h2.constant.ErrorCode;
 import org.h2.engine.Constants;
 import org.h2.engine.Session;
 import org.h2.message.Message;
@@ -70,7 +69,7 @@ public class LinkedIndex extends BaseIndex {
         String sql = buff.toString();
         synchronized (link.getConnection()) {
             try {
-                PreparedStatement prep = link.getPreparedStatement(sql);
+                PreparedStatement prep = link.getPreparedStatement(sql, false);
                 for (int i = 0, j = 0; i < row.getColumnCount(); i++) {
                     Value v = row.getValue(i);
                     if (v != null && v != ValueNull.INSTANCE) {
@@ -81,7 +80,7 @@ public class LinkedIndex extends BaseIndex {
                 prep.executeUpdate();
                 rowCount++;
             } catch (SQLException e) {
-                throw wrapException(sql, e);
+                throw link.wrapException(sql, e);
             }
         }
     }
@@ -119,7 +118,7 @@ public class LinkedIndex extends BaseIndex {
         String sql = buff.toString();
         synchronized (link.getConnection()) {
             try {
-                PreparedStatement prep = link.getPreparedStatement(sql);
+                PreparedStatement prep = link.getPreparedStatement(sql, true);
                 int j = 0;
                 for (int i = 0; first != null && i < first.getColumnCount(); i++) {
                     Value v = first.getValue(i);
@@ -136,9 +135,9 @@ public class LinkedIndex extends BaseIndex {
                     }
                 }
                 ResultSet rs = prep.executeQuery();
-                return new LinkedCursor(table, rs, session);
+                return new LinkedCursor(link, rs, session, sql, prep);
             } catch (SQLException e) {
-                throw wrapException(sql, e);
+                throw link.wrapException(sql, e);
             }
         }
     }
@@ -209,7 +208,7 @@ public class LinkedIndex extends BaseIndex {
         String sql = buff.toString();
         synchronized (link.getConnection()) {
             try {
-                PreparedStatement prep = link.getPreparedStatement(sql);
+                PreparedStatement prep = link.getPreparedStatement(sql, false);
                 for (int i = 0, j = 0; i < row.getColumnCount(); i++) {
                     Value v = row.getValue(i);
                     if (!isNull(v)) {
@@ -220,7 +219,7 @@ public class LinkedIndex extends BaseIndex {
                 int count = prep.executeUpdate();
                 rowCount -= count;
             } catch (SQLException e) {
-                throw wrapException(sql, e);
+                throw link.wrapException(sql, e);
             }
         }
     }
@@ -261,7 +260,7 @@ public class LinkedIndex extends BaseIndex {
         synchronized (link.getConnection()) {
             try {
                 int j = 1;
-                PreparedStatement prep = link.getPreparedStatement(sql);
+                PreparedStatement prep = link.getPreparedStatement(sql, false);
                 for (int i = 0; i < newRow.getColumnCount(); i++) {
                     newRow.getValue(i).set(prep, j);
                     j++;
@@ -277,15 +276,11 @@ public class LinkedIndex extends BaseIndex {
                 // this has no effect but at least it allows to debug the update count
                 rowCount = rowCount + count - count;
             } catch (SQLException e) {
-                throw wrapException(sql, e);
+                throw link.wrapException(sql, e);
             }
         }
     }
 
-    private SQLException wrapException(String sql, SQLException e) {
-        return Message.getSQLException(ErrorCode.ERROR_ACCESSING_LINKED_TABLE_2, new String[] { sql, e.toString() }, e);
-    }
-
     public long getRowCount(Session session) {
         return rowCount;
     }

h2/src/main/org/h2/table/TableLink.java

@@ -367,13 +367,29 @@ public class TableLink extends Table {
         }
     }
 
-    public long getRowCount(Session session) throws SQLException {
-        PreparedStatement prep = getPreparedStatement("SELECT COUNT(*) FROM " + qualifiedTableName);
+    public synchronized long getRowCount(Session session) throws SQLException {
+        String sql = "SELECT COUNT(*) FROM " + qualifiedTableName;
+        try {
+            PreparedStatement prep = getPreparedStatement(sql, false);
             ResultSet rs = prep.executeQuery();
             rs.next();
             long count = rs.getLong(1);
             rs.close();
             return count;
+        } catch (SQLException e) {
+            throw wrapException(sql, e);
+        }
+    }
+
+    /**
+     * Wrap a SQL exception that occurred while accessing a linked table.
+     *
+     * @param sql the SQL statement
+     * @param e the SQL exception from the remote database
+     * @return the wrapped SQL exception
+     */
+    public SQLException wrapException(String sql, SQLException e) {
+        return Message.getSQLException(ErrorCode.ERROR_ACCESSING_LINKED_TABLE_2, new String[] { sql, e.toString() }, e);
     }
 
     public String getQualifiedTable() {
@@ -384,10 +400,12 @@ public class TableLink extends Table {
      * Get a prepared statement object for the given statement. Prepared
      * statements are kept in a hash map to avoid re-creating them.
      *
-     * @param sql the SQL statement.
+     * @param sql the SQL statement
+     * @param exclusive if the prepared statement must be removed from the map
+     *          until reusePreparedStatement is called (only required for queries)
      * @return the prepared statement
      */
-    public PreparedStatement getPreparedStatement(String sql) throws SQLException {
+    public PreparedStatement getPreparedStatement(String sql, boolean exclusive) throws SQLException {
         Trace trace = database.getTrace(Trace.TABLE);
         if (trace.isDebugEnabled()) {
             trace.debug(getName() + ":\n" + sql);
@@ -400,6 +418,9 @@ public class TableLink extends Table {
             prep = conn.getConnection().prepareStatement(sql);
             prepared.put(sql, prep);
         }
+        if (exclusive) {
+            prepared.remove(sql);
+        }
         return prep;
     }
 
@@ -502,4 +523,8 @@ public class TableLink extends Table {
         return ROW_COUNT_APPROXIMATION;
     }
 
+    public void reusePreparedStatement(PreparedStatement prep, String sql) {
+        prepared.put(sql, prep);
+    }
+
 }

h2/src/test/org/h2/test/db/TestLinkedTable.java

@@ -34,6 +34,7 @@ public class TestLinkedTable extends TestBase {
 
     public void test() throws SQLException {
         // testLinkAutoAdd();
+        testNestedQueriesToSameTable();
         testSharedConnection();
         testMultipleSchemas();
         testReadOnlyLinkedTable();
@@ -66,6 +67,27 @@ public class TestLinkedTable extends TestBase {
 //        cb.close();
 //    }
 
+    private void testNestedQueriesToSameTable() throws SQLException {
+        if (config.memory || !SysProperties.SHARE_LINKED_CONNECTIONS) {
+            return;
+        }
+        org.h2.Driver.load();
+        deleteDb("linkedTable");
+        String url = getURL("linkedTable", true);
+        String user = getUser();
+        String password = getPassword();
+        Connection ca = getConnection(url, user, password);
+        Statement sa = ca.createStatement();
+        sa.execute("CREATE TABLE TEST(ID INT) AS SELECT 1");
+        ca.close();
+        Connection cb = DriverManager.getConnection("jdbc:h2:mem:two", "sa", "sa");
+        Statement sb = cb.createStatement();
+        sb.execute("CREATE LINKED TABLE T1(NULL, '" + url + "', '"+user+"', '"+password+"', 'TEST')");
+        sb.executeQuery("SELECT * FROM DUAL A LEFT OUTER JOIN T1 A ON A.ID=1 LEFT OUTER JOIN T1 B ON B.ID=1");
+        sb.execute("DROP ALL OBJECTS");
+        cb.close();
+    }
+
     private void testSharedConnection() throws SQLException {
         if (config.memory || !SysProperties.SHARE_LINKED_CONNECTIONS) {
             return;