Make the planner use indexes for sorting when doing a GROUP BY where

all of the GROUP BY columns are not mentioned in the select. Patch by Frederico (zepfred).

h2/src/docsrc/html/changelog.html

@@ -34,6 +34,8 @@ Change Log
     select * from dual join(select x from dual) on 1=1
 </li><li>Issue 598: parser fails on timestamp "24:00:00.1234" - prevent the creation of out-of-range time values.
 </li><li>Allow declaring triggers as source code (like functions). Patch by Sylvain CUAZ.
+</li><li>Make the planner use indexes for sorting when doing a GROUP BY where 
+    all of the GROUP BY columns are not mentioned in the select. Patch by Frederico (zepfred).
 </li></ul>
 
 <h2>Version 1.4.185 Beta (2015-01-16)</h2>

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

@@ -26,6 +26,7 @@ import org.h2.expression.Parameter;
 import org.h2.expression.Wildcard;
 import org.h2.index.Cursor;
 import org.h2.index.Index;
+import org.h2.index.IndexCondition;
 import org.h2.index.IndexType;
 import org.h2.message.DbException;
 import org.h2.result.LocalResult;
@@ -445,11 +446,16 @@ public class Select extends Query {
                     // with the exact same columns
                     IndexColumn idxCol = indexCols[j];
                     Column sortCol = sortCols[j];
+                    boolean implicitSortColumn = false;
                     if (idxCol.column != sortCol) {
+                        implicitSortColumn = isSortColumnImplicit(
+                                topTableFilter, idxCol.column);
+                        if (!implicitSortColumn) {
                             ok = false;
                             break;
                         }
-                    if (idxCol.sortType != sortTypes[j]) {
+                    }
+                    if (!implicitSortColumn && idxCol.sortType != sortTypes[j]) {
                         // NULL FIRST for ascending and NULLS LAST
                         // for descending would actually match the default
                         ok = false;
@@ -471,6 +477,43 @@ public class Select extends Query {
         return null;
     }
 
+    /**
+     * Validates the cases where ORDER BY clause do not contains all indexed
+     * columns, but the related index path still would be valid for such search.
+     * Sometimes, the absence of a column in the ORDER BY clause does not alter the
+     * expected final result, and an index sorted scan could still be used.
+     * <pre>
+     * CREATE TABLE test(a, b);
+     * CREATE UNIQUE INDEX idx_test ON test(a, b);
+     * SELECT b FROM test WHERE a=22 AND b>10 order by b;
+     * </pre>
+     * More restrictive rule where one table query with indexed column
+     * not present in the ORDER BY clause is filtered with equality conditions
+     * (at least one) of type COLUMN = CONSTANT in a conjunctive fashion.
+     * 
+     * @param sortColumn Column to be validated
+     * @return true if the column can be used implicitly, or false
+     *         otherwise.
+     */
+    private boolean isSortColumnImplicit(TableFilter tableFilter,
+            Column sortColumn) {
+        if (filters.size() == 1 && condition != null
+                && !condition.isDisjunctive()) {
+            ArrayList<IndexCondition> conditions = tableFilter
+                    .getIndexConditionsForColumn(sortColumn);
+            if (conditions.isEmpty()) {
+                return false;
+            }
+            for (IndexCondition conditionExp : conditions) {
+                if (!conditionExp.isEquality(true)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+        return false;
+    }
+
     private void queryDistinct(ResultTarget result, long limitRows) {
         // limitRows must be long, otherwise we get an int overflow
         // if limitRows is at or near Integer.MAX_VALUE

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

@@ -284,6 +284,11 @@ public class ConditionAndOr extends Condition {
         return left.getCost() + right.getCost();
     }
 
+    @Override
+    public boolean isDisjunctive() {
+        return andOrType == OR || left.isDisjunctive() || right.isDisjunctive();
+    }
+        
     /**
      * Get the left or the right sub-expression of this condition.
      *

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

@@ -191,6 +191,11 @@ public class ConditionIn extends Condition {
         return cost;
     }
 
+    @Override
+    public boolean isDisjunctive() {
+        return true;
+    }
+        
     /**
      * Add an additional element if possible. Example: given two conditions
      * A IN(1, 2) OR A=3, the constant 3 is added: A IN(1, 2, 3).

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

@@ -147,6 +147,11 @@ public class ConditionInConstantSet extends Condition {
         return cost;
     }
 
+    @Override
+    public boolean isDisjunctive() {
+        return true;
+    }        
+
     /**
      * Add an additional element if possible. Example: given two conditions
      * A IN(1, 2) OR A=3, the constant 3 is added: A IN(1, 2, 3).

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

@@ -184,4 +184,8 @@ public class ConditionInSelect extends Condition {
         filter.addIndexCondition(IndexCondition.getInQuery(l, query));
     }
 
+    @Override
+    public boolean isDisjunctive() {
+        return true;
+   }
 }

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

@@ -262,6 +262,15 @@ public abstract class Expression {
         return this;
     }
 
+    /**
+     * Allows to check if the related expression is under conjunctive format.
+     * 
+     * @return if the related expression has the logic operator OR.
+     */
+    public boolean isDisjunctive(){
+        return false;
+    }
+
     /**
      * Add conditions to a table filter if they can be evaluated.
      *

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

@@ -332,6 +332,22 @@ public class IndexCondition {
         }
     }
 
+    /**     
+     * Check if this index condition is of the type equality.
+     *
+     * @param constantExpression if the inner node is a constant expression      
+     * @return true if this is a equality condition
+     */
+    public boolean isEquality(boolean constantExpression){
+        switch (compareType) {
+        case Comparison.EQUAL:
+        case Comparison.EQUAL_NULL_SAFE:            
+            return !constantExpression || expression.isConstant();        
+        default:
+            return false;
+        }
+    }
+    
     public int getCompareType() {
         return compareType;
     }

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

@@ -486,6 +486,22 @@ public class TableFilter implements ColumnResolver {
         indexConditions.add(condition);
     }
 
+    /**
+     * Return a list of index condition filtered by a specific column.
+     * 
+     * @param column The column of the condition
+     * @return the filtered list
+     */
+    public ArrayList<IndexCondition> getIndexConditionsForColumn(Column column){
+        ArrayList<IndexCondition> conditions = New.arrayList(indexConditions.size());
+        for (IndexCondition condition: indexConditions){
+            if (column.equals(condition.getColumn())){
+                conditions.add(condition);
+            }
+        }
+        return conditions;
+    }
+
     /**
      * Add a filter condition.
      *

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

@@ -62,6 +62,7 @@ public class TestOptimizations extends TestBase {
         testNestedInSelect();
         testInSelectJoin();
         testMinMaxNullOptimization();
+        testUseIndexWhenAllColumnsNotInOrderBy();
         if (config.networked) {
             return;
         }
@@ -669,6 +670,22 @@ public class TestOptimizations extends TestBase {
         conn.close();
     }
     
+    private void testUseIndexWhenAllColumnsNotInOrderBy() throws SQLException {
+        deleteDb("optimizations");
+        Connection conn = getConnection("optimizations");
+        Statement stat = conn.createStatement();
+        stat.execute("CREATE TABLE test(id INT PRIMARY KEY, account INT, txid INT);"); 
+        stat.execute("INSERT INTO test SELECT x, x*100, x FROM SYSTEM_RANGE(1, 10000);");
+        stat.execute("ANALYZE SAMPLE_SIZE 5");
+        stat.execute("CREATE UNIQUE INDEX idx_test_account_txid ON test(account, txid DESC);");
+        ResultSet rs;
+        rs = stat.executeQuery("EXPLAIN ANALYZE SELECT txid FROM test WHERE account=22 AND txid<9999999 ORDER BY txid DESC LIMIT 25");
+        rs.next();
+        String plan = rs.getString(1);
+        assertContains(plan, "index sorted");
+        conn.close();
+    }
+
     private void testDistinctOptimization() throws SQLException {
         deleteDb("optimizations");
         Connection conn = getConnection("optimizations");