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h2/src/main/org/h2/command/Parser.java

@@ -109,6 +109,7 @@ import org.h2.expression.ValueExpression;
 import org.h2.expression.Wildcard;
 import org.h2.index.Index;
 import org.h2.message.Message;
+import org.h2.result.SortOrder;
 import org.h2.schema.Schema;
 import org.h2.schema.Sequence;
 import org.h2.schema.TriggerObject;
@@ -137,6 +138,9 @@ import org.h2.value.ValueString;
 import org.h2.value.ValueTime;
 import org.h2.value.ValueTimestamp;
 
+/**
+ * The parser is used to convert a SQL statement string to an command object.
+ */
 public class Parser {
 
     // used during the tokenizer phase
@@ -678,9 +682,18 @@ public class Parser {
             columns.add(column);
             if (readIf("ASC")) {
                  // ignore
+            } else if (readIf("DESC")) {
+                column.sortType = SortOrder.DESCENDING;
+            }
+            if (readIf("NULLS")) {
+                if (readIf("FIRST")) {
+                    column.sortType |= SortOrder.NULLS_FIRST;
                 } else {
-                readIf("DESC");
-                column.descending = true;
+                    read("LAST");
+                    column.sortType |= SortOrder.NULLS_LAST;
+                }
+            } else {
+                
             }
         } while (readIf(","));
         read(")");

h2/src/main/org/h2/command/dml/Optimizer.java

@@ -15,6 +15,9 @@ import org.h2.table.PlanItem;
 import org.h2.table.TableFilter;
 import org.h2.util.Permutations;
 
+/**
+ * The optimizer is responsible to find the best execution plan for a given query.
+ */
 public class Optimizer {
 
     private static final int MAX_BRUTE_FORCE_FILTERS = 7;

h2/src/main/org/h2/command/dml/Select.java

@@ -22,6 +22,7 @@ import org.h2.result.LocalResult;
 import org.h2.result.SortOrder;
 import org.h2.table.Column;
 import org.h2.table.ColumnResolver;
+import org.h2.table.IndexColumn;
 import org.h2.table.Table;
 import org.h2.table.TableFilter;
 import org.h2.util.ObjectArray;
@@ -32,6 +33,8 @@ import org.h2.value.ValueArray;
 import org.h2.value.ValueNull;
 
 /**
+ * This class represents a simple SELECT statement.
+ * 
  * visibleColumnCount <= distinctColumnCount <= expressionCount
  * Sortable count could include ORDER BY expressions that are not in the select list
  * Expression count could include GROUP BY expressions
@@ -60,6 +63,7 @@ public class Select extends Query {
     private double cost;
     private boolean isQuickQuery;
     private boolean isPrepared, checkInit;
+    private boolean sortUsingIndex;
     private SortOrder sort;
 
     public Select(Session session) {
@@ -190,16 +194,18 @@ public class Select extends Query {
         }
     }
 
+    /**
+     * Get the index that matches the ORDER BY list, if one exists.
+     * This is to avoid running a separate ORDER BY if an index can be used.
+     * This is specially important for large result sets, if only the first few rows are important
+     * (LIMIT is used)
+     * 
+     * @return the index if one is found
+     */
     private Index getSortIndex() throws SQLException {
         if (sort == null) {
             return null;
         }
-        int[] sortTypes = sort.getSortTypes();
-        for (int i = 0; i < sortTypes.length; i++) {
-            if ((sortTypes[i] & (SortOrder.DESCENDING | SortOrder.NULLS_LAST)) != 0) {
-                return null;
-            }
-        }
         int[] indexes = sort.getIndexes();
         ObjectArray sortColumns = new ObjectArray();
         for (int i = 0; i < indexes.length; i++) {
@@ -223,6 +229,7 @@ public class Select extends Query {
         }
         Column[] sortCols = new Column[sortColumns.size()];
         sortColumns.toArray(sortCols);
+        int[] sortTypes = sort.getSortTypes();
         if (sortCols.length == 0) {
             // sort just on constants - can use scan index
             return topTableFilter.getTable().getScanIndex(session);
@@ -237,15 +244,22 @@ public class Select extends Query {
             if (index.getIndexType().isHash()) {
                 continue;
             }
-            Column[] indexCols = index.getColumns();
+            IndexColumn[] indexCols = index.getIndexColumns();
             if (indexCols.length < sortCols.length) {
                 continue;
             }
             boolean ok = true;
             for (int j = 0; j < sortCols.length; j++) {
-                // the index and the sort order must start with the exact same
-                // columns
-                if (indexCols[j] != sortCols[j]) {
+                // the index and the sort order must start 
+                // with the exact same columns
+                IndexColumn idxCol = indexCols[j];
+                Column sortCol = sortCols[j];
+                if (idxCol.column != sortCol) {
+                    ok = false;
+                    break;
+                }
+                if (idxCol.sortType != sortTypes[j]) {
+                    // TODO NULL FIRST for ascending and NULLS LAST for descending would actually match the default
                     ok = false;
                     break;
                 }
@@ -274,7 +288,7 @@ public class Select extends Query {
                 }
                 result.addRow(row);
                 rowNumber++;
-                if (sort == null && limitRows != 0 && result.getRowCount() >= limitRows) {
+                if ((sort == null || sortUsingIndex) && limitRows != 0 && result.getRowCount() >= limitRows) {
                     break;
                 }
                 if (sampleSize > 0 && rowNumber >= sampleSize) {
@@ -311,7 +325,9 @@ public class Select extends Query {
         }
         int columnCount = expressions.size();
         LocalResult result = new LocalResult(session, expressions, visibleColumnCount);
+        if (!sortUsingIndex) {
             result.setSortOrder(sort);
+        }
         if (distinct) {
             result.setDistinct();
         }
@@ -489,7 +505,7 @@ public class Select extends Query {
             Index current = topTableFilter.getIndex();
             if (index != null && (current.getIndexType().isScan() || current == index)) {
                 topTableFilter.setIndex(index);
-                sort = null;
+                sortUsingIndex = true;
             }
         }
     }

h2/src/main/org/h2/engine/Constants.java

@@ -64,6 +64,9 @@ import org.h2.constant.SysProperties;
  * 
  * @author Thomas
  */
+/**
+ * Constants are fixed values that are used in the whole database code.
+ */
 public class Constants {
 
     public static final int BUILD_ID = 60;
@@ -82,9 +85,6 @@ public class Constants {
         return VERSION_MAJOR + "." + VERSION_MINOR + "." + BUILD_ID + " (" + BUILD + ")";
     }
 
-    public static final int NULL_SORT_LOW = 1, NULL_SORT_HIGH = 2;
-    public static final int NULL_SORT_START = 3, NULL_SORT_END = 4;
-    public static final int NULL_SORT_DEFAULT = NULL_SORT_LOW;
     public static final int DEFAULT_SERVER_PORT = 9092; // this is also in the docs
     public static final String START_URL = "jdbc:h2:";
     public static final String URL_FORMAT = START_URL + "{ {.|mem:}[name] | [file:]fileName | {tcp|ssl}:[//]server[:port][,server2[:port]]/name }[;key=value...]";

h2/src/main/org/h2/engine/Database.java

@@ -59,10 +59,11 @@ import org.h2.value.Value;
 import org.h2.value.ValueInt;
 
 /**
+ * There is one database object per open database.
+ * 
  * @author Thomas
  * @since 2004-04-15 22:49
  */
-
 /*
  * MetaData format: int id int headPos (for indexes) int objectType String sql
  */

h2/src/main/org/h2/engine/DatabaseCloser.java

@@ -6,6 +6,9 @@ package org.h2.engine;
 
 import java.lang.ref.WeakReference;
 
+/**
+ * This class is reponsible to close a database if the application did not close a connection.
+ */
 public class DatabaseCloser extends Thread {
 
     private final boolean shutdownHook;
@@ -52,13 +55,14 @@ public class DatabaseCloser extends Thread {
                 return;
             }
         }
+        Database database = null;
         synchronized (this) {
             if (databaseRef != null) {
-                Database database = (Database) databaseRef.get();
-                if (database != null) {
-                    database.close(shutdownHook);
+                database = (Database) databaseRef.get();
             }
         }
+        if (database != null) {
+            database.close(shutdownHook);
         }
     }
 

h2/src/main/org/h2/expression/Aggregate.java

@@ -161,6 +161,10 @@ public class Aggregate extends Expression {
             case MAX:
                 boolean first = type == MIN;
                 Index index = getColumnIndex(first);
+                int sortType = index.getIndexColumns()[0].sortType;
+                if ((sortType & SortOrder.DESCENDING) != 0) {
+                    first = !first;
+                }
                 SearchRow row = index.findFirstOrLast(session, first);
                 Value v;
                 if (row == null) {

h2/src/main/org/h2/expression/Comparison.java

@@ -19,7 +19,7 @@ import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * Example comparison expressions are ID=1, NAME=NAME, NAME IS NULL.
  */
 public class Comparison extends Condition {
 

h2/src/main/org/h2/expression/Expression.java

@@ -15,7 +15,7 @@ import org.h2.value.Value;
 
 
 /**
- * @author Thomas
+ * An expression is a operation, a value, or a function in a query.
  */
 public abstract class Expression {
     

h2/src/main/org/h2/expression/ExpressionColumn.java

@@ -22,9 +22,6 @@ import org.h2.table.TableFilter;
 import org.h2.value.Value;
 import org.h2.value.ValueBoolean;
 
-/**
- * @author Thomas
- */
 public class ExpressionColumn extends Expression {
     private Database database;
     private String schemaName;

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

@@ -14,6 +14,7 @@ import org.h2.message.Message;
 import org.h2.message.Trace;
 import org.h2.result.Row;
 import org.h2.result.SearchRow;
+import org.h2.result.SortOrder;
 import org.h2.schema.SchemaObjectBase;
 import org.h2.table.Column;
 import org.h2.table.IndexColumn;
@@ -23,7 +24,7 @@ import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * Most index implementations extend the base index.
  */
 public abstract class BaseIndex extends SchemaObjectBase implements Index {
 
@@ -90,7 +91,7 @@ public abstract class BaseIndex extends SchemaObjectBase implements Index {
 
     public abstract void truncate(Session session) throws SQLException;
 
-    public abstract boolean canGetFirstOrLast(boolean first);
+    public abstract boolean canGetFirstOrLast();
 
     public abstract SearchRow findFirstOrLast(Session session, boolean first) throws SQLException;
 
@@ -144,14 +145,14 @@ public abstract class BaseIndex extends SchemaObjectBase implements Index {
     }
 
     public int compareRows(SearchRow rowData, SearchRow compare) throws SQLException {
-        for (int i = 0; i < columns.length; i++) {
+        for (int i = 0; i < indexColumns.length; i++) {
             int index = columnIds[i];
             Value v = compare.getValue(index);
             if (v == null) {
                 // can't compare further
                 return 0;
             }
-            int c = compareValues(rowData.getValue(index), v);
+            int c = compareValues(rowData.getValue(index), v, indexColumns[i].sortType);
             if (c != 0) {
                 return c;
             }
@@ -179,17 +180,19 @@ public abstract class BaseIndex extends SchemaObjectBase implements Index {
         return k1 > k2 ? 1 : -1;
     }
 
-    private int compareValues(Value v1, Value v2) throws SQLException {
-        if (v1 == null) {
-            if (v2 == null) {
+    private int compareValues(Value a, Value b, int sortType) throws SQLException {
+        boolean aNull = a == null, bNull = b == null;
+        if (aNull || bNull) {
+            if (aNull == bNull) {
                 return 0;
             }
-            return 1;
+            return SortOrder.compareNull(aNull, bNull, sortType);
         }
-        if (v2 == null) {
-            return -1;
+        int comp = database.compareTypeSave(a, b);
+        if ((sortType & SortOrder.DESCENDING) != 0) {
+            comp = -comp;
         }
-        return database.compareTypeSave(v1, v2);
+        return comp;
     }
 
     public int getColumnIndex(Column col) {

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

@@ -25,7 +25,7 @@ import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * This is the most common type of index, a b tree index.
  */
 public class BtreeIndex extends BaseIndex implements RecordReader {
 
@@ -284,7 +284,7 @@ public class BtreeIndex extends BaseIndex implements RecordReader {
         return lastChange;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return true;
     }
 

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

@@ -65,7 +65,7 @@ public class FunctionIndex extends BaseIndex {
         throw Message.getUnsupportedException();
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -142,7 +142,7 @@ public class HashIndex extends BaseIndex {
         return true;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -36,7 +36,7 @@ public interface Index extends SchemaObject {
 
     void truncate(Session session) throws SQLException;
 
-    boolean canGetFirstOrLast(boolean first);
+    boolean canGetFirstOrLast();
 
     SearchRow findFirstOrLast(Session session, boolean first) throws SQLException;
 

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

@@ -15,9 +15,9 @@ import org.h2.message.Message;
 import org.h2.table.Column;
 import org.h2.value.Value;
 
-
 /**
- * @author Thomas
+ * A index condition object is made for each condition that can potentially use an index.
+ * This class does not extend expression, but in general there is one expression that maps to each index condition.
  */
 public class IndexCondition {
     public static final int EQUALITY = 1, START = 2, END = 4, RANGE = START | END, ALWAYS_FALSE = 8;

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

@@ -532,7 +532,7 @@ public class LinearHashIndex extends BaseIndex implements RecordReader {
         return bucketSize;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -157,7 +157,7 @@ public class LinkedIndex extends BaseIndex {
         return false;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -82,7 +82,7 @@ public class MetaIndex extends BaseIndex {
         return null;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -120,9 +120,6 @@ public class MultiVersionCursor implements Cursor {
                             return true;
                         }
                     }
-int test;
-this.index.debug("error", session, deltaRow);
-System.exit(1);
                     throw Message.getInternalError();
                 }
                 int compare = index.compareRows(deltaRow, baseRow);

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

@@ -33,8 +33,6 @@ public class MultiVersionIndex implements Index {
     }
 
     public void add(Session session, Row row) throws SQLException {
-int test;
-debug("add", session, row);
         synchronized (sync) {
             base.add(session, row);
             if (removeIfExists(session, row)) {
@@ -53,8 +51,6 @@ debug("add", session, row);
     }
 
     public Cursor find(Session session, SearchRow first, SearchRow last) throws SQLException {
-int test;
-debug("find", session, first); 
         synchronized (sync) {
             Cursor baseCursor = base.find(session, first, last);
             Cursor deltaCursor = delta.find(session, first, last);
@@ -62,7 +58,7 @@ debug("find", session, first);
         }
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         // TODO in many cases possible, but more complicated
         return false;
     }
@@ -80,26 +76,19 @@ debug("find", session, first);
     }
     
     private boolean removeIfExists(Session session, Row row) throws SQLException {
-int test;
-debug("removeIfExists ", session, row);
         // maybe it was inserted by the same session just before
         Cursor c = delta.find(session, row, row);
         while (c.next()) {
             Row r = c.get();
             if (r.getPos() == row.getPos()) {
-debug("  >remove", session, null);
                 delta.remove(session, row);
-debug("  >return true", session, null);
                 return true;
             }
         }
-debug("  >return false", session, null);
         return false;
     }
 
     public void remove(Session session, Row row) throws SQLException {
-int test;
-debug("remove", session, row);
         synchronized (sync) {
             base.remove(session, row);
             if (removeIfExists(session, row)) {
@@ -117,8 +106,6 @@ debug("remove", session, row);
     }
 
     public void truncate(Session session) throws SQLException {
-int test;
-debug("truncate", session, null);
         synchronized (sync) {
             delta.truncate(session);
             base.truncate(session);
@@ -126,8 +113,6 @@ debug("truncate", session, null);
     }
     
     public void commit(int operation, Row row) throws SQLException {
-int test;
-debug("commit", null, row);
         synchronized (sync) {
             removeIfExists(null, row);
         }
@@ -273,7 +258,7 @@ debug("commit", null, row);
     }
     
     void debug(String s, Session session, SearchRow row) throws SQLException {
-//        System.out.println(this + " " + s + " sess:" + (session == null ? -1: session.getId()) + " " + (row == null ? "" : row.getValue(0).getString()));
+        // System.out.println(this + " " + s + " sess:" + (session == null ? -1: session.getId()) + " " + (row == null ? "" : row.getValue(0).getString()));
     }
 
 }

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

@@ -66,7 +66,7 @@ public class RangeIndex extends BaseIndex {
         throw Message.getUnsupportedException();
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return true;
     }
 

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

@@ -253,7 +253,7 @@ public class ScanIndex extends BaseIndex {
         return false;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

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

@@ -341,7 +341,7 @@ public class TreeIndex extends BaseIndex {
         return true;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return true;
     }
 

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

@@ -21,6 +21,11 @@ import org.h2.util.ObjectArray;
 import org.h2.util.SmallLRUCache;
 import org.h2.value.Value;
 
+/**
+ * This object represents a virtual index for a query.
+ * Actually it only represents a prepared statement that is
+ * a SELECT statement.
+ */
 public class ViewIndex extends BaseIndex {
 
     private String querySQL;
@@ -233,7 +238,7 @@ public class ViewIndex extends BaseIndex {
         return false;
     }
 
-    public boolean canGetFirstOrLast(boolean first) {
+    public boolean canGetFirstOrLast() {
         return false;
     }
 

h2/src/main/org/h2/jdbc/JdbcDatabaseMetaData.java

@@ -420,41 +420,41 @@ public class JdbcDatabaseMetaData extends TraceObject implements DatabaseMetaDat
     /**
      * Checks is NULL values are sorted high (bigger than any non-null values).
      *
-     * @return true or false
+     * @return false
      */
     public boolean nullsAreSortedHigh() {
         debugCodeCall("nullsAreSortedHigh");
-        return Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_HIGH;
+        return false;
     }
 
     /**
      * Checks is NULL values are sorted low (smaller than any non-null values).
      *
-     * @return true or false
+     * @return true
      */
     public boolean nullsAreSortedLow() {
         debugCodeCall("nullsAreSortedLow");
-        return Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_LOW;
+        return true;
     }
 
     /**
      * Checks is NULL values are sorted at the beginning (no matter if ASC or DESC is used).
      *
-     * @return true or false
+     * @return false
      */
     public boolean nullsAreSortedAtStart() {
         debugCodeCall("nullsAreSortedAtStart");
-        return Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_START;
+        return false;
     }
 
     /**
      * Checks is NULL values are sorted at the end (no matter if ASC or DESC is used).
      *
-     * @return true or false
+     * @return false
      */
     public boolean nullsAreSortedAtEnd() {
         debugCodeCall("nullsAreSortedAtEnd");
-        return Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_END;
+        return false;
     }
 
     /**

h2/src/main/org/h2/result/SortOrder.java

@@ -6,7 +6,6 @@ package org.h2.result;
 
 import java.sql.SQLException;
 
-import org.h2.engine.Constants;
 import org.h2.engine.Database;
 import org.h2.expression.Expression;
 import org.h2.util.ObjectArray;
@@ -15,10 +14,10 @@ import org.h2.util.StringUtils;
 import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
+
 /**
- * @author Thomas
+ * A sort order represents an ORDER BY clause in a query.
  */
-
 public class SortOrder {
     public static final int ASCENDING = 0, DESCENDING = 1;
     public static final int NULLS_FIRST = 2, NULLS_LAST = 4;
@@ -61,38 +60,32 @@ public class SortOrder {
         return buff.toString();
     }
     
-    public int compare(Value[] a, Value[] b) throws SQLException {
-        for (int i = 0; i < len; i++) {
-            int idx = indexes[i];
-            int type = sortTypes[i];
-            Value o1 = a[idx];
-            Value o2 = b[idx];
-            boolean b1 = o1 == ValueNull.INSTANCE, b2 = o2 == ValueNull.INSTANCE;
-            if (b1 || b2) {
-                if (b1 == b2) {
-                    continue;
-                }
+    public static int compareNull(boolean aNull, boolean bNull, int type) {
         if ((type & NULLS_FIRST) != 0) {
-                    return b1 ? -1 : 1;
+            return aNull ? -1 : 1;
         } else if ((type & NULLS_LAST) != 0) {
-                    return b1 ? 1 : -1;
+            return aNull ? 1 : -1;
         } else {
-                    // this depends on NULL_SORT_DEFAULT
-                    int comp;
-                    if (Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_LOW) {
-                        comp = b1 ? -1 : 1;
-                        return (type & DESCENDING) == 0 ? comp : -comp;
-                    } else if (Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_HIGH) {
-                        comp = b1 ? 1 : -1;
+            // see also JdbcDatabaseMetaData.nullsAreSorted*
+            int comp = aNull ? -1 : 1;
             return (type & DESCENDING) == 0 ? comp : -comp;
-                    } else if (Constants.NULL_SORT_DEFAULT == Constants.NULL_SORT_START) {
-                        return b1 ? 1 : -1;
-                    } else {
-                        return b1 ? -1 : 1;
         }
     }
+
+    public int compare(Value[] a, Value[] b) throws SQLException {
+        for (int i = 0; i < len; i++) {
+            int idx = indexes[i];
+            int type = sortTypes[i];
+            Value ao = a[idx];
+            Value bo = b[idx];
+            boolean aNull = ao == ValueNull.INSTANCE, bNull = bo == ValueNull.INSTANCE;
+            if (aNull || bNull) {
+                if (aNull == bNull) {
+                    continue;
+                }
+                return compareNull(aNull, bNull, type);
             }
-            int comp = database.compare(o1, o2);
+            int comp = database.compare(ao, bo);
             if (comp != 0) {
                 return (type & DESCENDING) == 0 ? comp : -comp;
             }

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

@@ -33,7 +33,7 @@ import org.h2.value.ValueTimestamp;
 import org.h2.value.ValueUuid;
 
 /**
- * @author Thomas
+ * This class represents a column in a table.
  */
 public class Column {
     private final int type;

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

@@ -9,6 +9,10 @@ import java.sql.SQLException;
 import org.h2.command.dml.Select;
 import org.h2.value.Value;
 
+/**
+ * A column resolver is list of column (for example, a table) that can map a 
+ * column name to an actual column.
+ */
 public interface ColumnResolver {
 
     String getTableAlias();

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

@@ -6,16 +6,27 @@ package org.h2.table;
 
 import java.sql.SQLException;
 
+import org.h2.result.SortOrder;
+
+/**
+ * This represents a column item of an index. This is required because some 
+ * indexes support descending sorted columns.
+ */
 public class IndexColumn {
     public String columnName;
     public Column column;
-    public boolean descending;
+    public int sortType = SortOrder.ASCENDING;
     
     public String getSQL() {
         StringBuffer buff = new StringBuffer(column.getSQL());
-        if (descending) {
+        if ((sortType & SortOrder.DESCENDING) != 0) {
             buff.append(" DESC");
         }
+        if ((sortType & SortOrder.NULLS_FIRST) != 0) {
+            buff.append(" NULLS FIRST");
+        } else if ((sortType & SortOrder.NULLS_LAST) != 0) {
+            buff.append(" NULLS LAST");
+        }
         return buff.toString();
     }
     

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

@@ -22,6 +22,7 @@ import org.h2.result.Row;
 import org.h2.result.SearchRow;
 import org.h2.result.SimpleRow;
 import org.h2.result.SimpleRowValue;
+import org.h2.result.SortOrder;
 import org.h2.schema.Schema;
 import org.h2.schema.SchemaObjectBase;
 import org.h2.schema.Sequence;
@@ -32,9 +33,8 @@ import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * A table contains a list of columns and a list of rows.
  */
-
 public abstract class Table extends SchemaObjectBase {
     
     public static final int TYPE_CACHED = 0, TYPE_MEMORY = 1;
@@ -489,7 +489,12 @@ public abstract class Table extends SchemaObjectBase {
         ObjectArray indexes = getIndexes();
         for (int i = 1; indexes != null && i < indexes.size(); i++) {
             Index index = (Index) indexes.get(i);
-            if (index.canGetFirstOrLast(first)) {
+            if (index.canGetFirstOrLast()) {
+                IndexColumn idxCol = index.getIndexColumns()[0];
+                if ((idxCol.sortType & SortOrder.DESCENDING) != 0 && (idxCol.sortType & SortOrder.NULLS_FIRST) == 0) {
+                    // for descending sorted columns, if the NULLs are at the end, it does not work for some index types
+                    continue;
+                }
                 int idx = index.getColumnIndex(column);
                 if (idx == 0) {
                     return index;

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

@@ -20,13 +20,16 @@ import org.h2.index.IndexCondition;
 import org.h2.message.Message;
 import org.h2.result.Row;
 import org.h2.result.SearchRow;
+import org.h2.result.SortOrder;
 import org.h2.util.ObjectArray;
 import org.h2.util.StringUtils;
 import org.h2.value.Value;
 import org.h2.value.ValueInt;
 
 /**
- * @author Thomas
+ * A table filter represents a table that is used in a query. There is one such object whenever a table
+ * (or view) is used in a query. For example the following query has 2 table filters:
+ * SELECT * FROM TEST T1, TEST T2.
  */
 public class TableFilter implements ColumnResolver {
     private static final int BEFORE_FIRST = 0, FOUND = 1, AFTER_LAST = 2, NULL_ROW = 3;
@@ -35,6 +38,7 @@ public class TableFilter implements ColumnResolver {
     private final Select select;
     private Session session;
     private Index index;
+    private IndexColumn[] indexColumns;
     private Cursor cursor;
     private int scanCount;
     private boolean used; // used in the plan
@@ -134,7 +138,7 @@ public class TableFilter implements ColumnResolver {
     }
 
     public void setPlanItem(PlanItem item) {
-        this.index = item.getIndex();
+        setIndex(item.getIndex());
         for (int i = 0; joins != null && i < joins.size(); i++) {
             TableFilter join = getTableFilter(i);
             if (item.getJoinPlan() != null) {
@@ -204,17 +208,24 @@ public class TableFilter implements ColumnResolver {
                 int type = column.getType();
                 int id = column.getColumnId();
                 Value v = condition.getCurrentValue(session).convertTo(type);
-                if (condition.isStart()) {
-                    // TODO index: start.setExpression(id,
-                    // bigger(start.getValue(id), e));
+                boolean isStart = condition.isStart(), isEnd = condition.isEnd();
+                IndexColumn idxCol = indexColumns[id];
+                if (idxCol != null && (idxCol.sortType & SortOrder.DESCENDING) != 0) {
+                    // if the index column is sorted the other way, we swap end and start
+                    // NULLS_FIRST / NULLS_LAST is not a problem, as nulls never match anyway
+                    boolean temp = isStart;
+                    isStart = isEnd;
+                    isEnd = temp;
+                }
+                if (isStart) {
+                    // TODO index: start.setExpression(id, bigger(start.getValue(id), e));
                     if (start == null) {
                         start = table.getTemplateRow();
                     }
                     start.setValue(id, v);
                 }
-                if (condition.isEnd()) {
-                    // TODO index: end.setExpression(id,
-                    // smaller(end.getExpression(id), e));
+                if (isEnd) {
+                    // TODO index: end.setExpression(id, smaller(end.getExpression(id), e));
                     if (end == null) {
                         end = table.getTemplateRow();
                     }
@@ -459,6 +470,17 @@ public class TableFilter implements ColumnResolver {
 
     public void setIndex(Index index) {
         this.index = index;
+        Column[] columns = table.getColumns();
+        indexColumns = new IndexColumn[columns.length];
+        IndexColumn[] idxCols = index.getIndexColumns();
+        if (idxCols != null) {
+            for (int i = 0; i < columns.length; i++) {
+                int idx = index.getColumnIndex(columns[i]);
+                if (idx >= 0) {
+                    indexColumns[i] = idxCols[idx];
+                }
+            }
+        }
     }
 
     public void setUsed(boolean used) {

h2/src/test/org/h2/test/TestAll.java

@@ -7,7 +7,6 @@ package org.h2.test;
 import java.sql.SQLException;
 import java.util.Properties;
 
-import org.h2.constant.SysProperties;
 import org.h2.server.TcpServer;
 import org.h2.test.db.TestAutoRecompile;
 import org.h2.test.db.TestBackup;
@@ -142,10 +141,12 @@ java org.h2.test.TestAll timer
 
 /*
 
+
 ----
 A file is sent although the Japanese translation has not been completed yet.
 ----
 
+reverse index 
 Code coverage
 
 At startup, when corrupted, say if LOG=0 was used before

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

@@ -41,6 +41,7 @@ public class TestCluster extends TestBase {
             prep.setString(2, "Data" + i);
             prep.executeUpdate();
         }
+        check(conn, len);        
         conn.close();
 
         CreateCluster.main(new String[] { "-urlSource", "jdbc:h2:file:" + baseDir + "/node1/test", "-urlTarget",

h2/src/test/org/h2/test/testSimple.in.txt

+CREATE TABLE TEST(ID INT);
+INSERT INTO TEST VALUES(1), (2), (3);
+create index idxdesc on test(id desc);
+select * from test where id between 0 and 1;
+> 1;
+select * from test where id between 3 and 4;
+> 3;
+drop table test;
+
 CREATE TABLE TEST(ID INT PRIMARY KEY, NAME VARCHAR(255));
 INSERT INTO TEST VALUES(1, 'Hello'), (2, 'HelloWorld'), (3, 'HelloWorldWorld');
 SELECT COUNT(*) FROM TEST WHERE NAME REGEXP 'World';