New database setting OPTIMIZE_IN_SELECT (enabled by default for version 1.3.x).…

New database setting OPTIMIZE_IN_SELECT (enabled by default for version 1.3.x). If enabled, IN(SELECT...) conditions are faster if there are many rows in the table or subquery.

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

@@ -20,7 +20,6 @@ import org.h2.expression.Parameter;
 import org.h2.expression.ValueExpression;
 import org.h2.message.DbException;
 import org.h2.result.LocalResult;
-import org.h2.result.ResultInterface;
 import org.h2.result.ResultTarget;
 import org.h2.result.SortOrder;
 import org.h2.table.ColumnResolver;
@@ -223,7 +222,7 @@ public abstract class Query extends Prepared {
         return params;
     }
 
-    public ResultInterface query(int maxrows) {
+    public LocalResult query(int maxrows) {
         return query(maxrows, null);
     }
 
@@ -234,7 +233,7 @@ public abstract class Query extends Prepared {
      * @param target the target result (null will return the result)
      * @return the result set (if the target is not set).
      */
-    ResultInterface query(int limit, ResultTarget target) {
+    LocalResult query(int limit, ResultTarget target) {
         fireBeforeSelectTriggers();
         if (!session.getDatabase().getOptimizeReuseResults()) {
             return queryWithoutCache(limit, target);

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

@@ -372,7 +372,7 @@ public class SelectUnion extends Query {
         return buff.toString();
     }
 
-    public ResultInterface query(int limit, ResultTarget target) {
+    public LocalResult query(int limit, ResultTarget target) {
         // union doesn't always know the parameter list of the left and right queries
         return queryWithoutCache(limit, target);
     }

h2/src/main/org/h2/constant/DbSettings.java

@@ -195,6 +195,13 @@ public class DbSettings extends SettingsBase {
      */
     public final boolean optimizeInList = get("OPTIMIZE_IN_LIST", true);
 
+    /**
+     * Database setting <code>OPTIMIZE_IN_SELECT</code> (default: false).<br />
+     * Optimize IN(SELECT ...) comparisons. This includes
+     * optimization for SELECT, DELETE, and UPDATE.
+     */
+    public final boolean optimizeInSelect = get("OPTIMIZE_IN_SELECT", Constants.VERSION_MINOR >= 3);
+
     /**
      * Database setting <code>OPTIMIZE_IS_NULL</code> (default: false).<br />
      * Use an index for condition of the form columnName IS NULL.

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

@@ -12,7 +12,7 @@ import org.h2.engine.Database;
 import org.h2.engine.Session;
 import org.h2.index.IndexCondition;
 import org.h2.message.DbException;
-import org.h2.result.ResultInterface;
+import org.h2.result.LocalResult;
 import org.h2.table.ColumnResolver;
 import org.h2.table.TableFilter;
 import org.h2.util.StringUtils;
@@ -24,6 +24,7 @@ import org.h2.value.ValueNull;
  * An 'in' condition with a subquery, as in WHERE ID IN(SELECT ...)
  */
 public class ConditionInSelect extends Condition {
+
     private Database database;
     private Expression left;
     private Query query;
@@ -41,11 +42,36 @@ public class ConditionInSelect extends Condition {
 
     public Value getValue(Session session) {
         query.setSession(session);
-        ResultInterface rows = query.query(0);
+        LocalResult rows = query.query(0);
         session.addTemporaryResult(rows);
+        Value l = left.getValue(session);
+        if (!session.getDatabase().getSettings().optimizeInSelect) {
+            return getValueSlow(rows, l);
+        }
+        if (compareType != Comparison.EQUAL && compareType != Comparison.EQUAL_NULL_SAFE) {
+            return getValueSlow(rows, l);
+        }
+        if (rows.getRowCount() == 0) {
+            return ValueBoolean.get(false);
+        }
+        if (l == ValueNull.INSTANCE) {
+            return l;
+        }
+        if (all && rows.getRowCount() > 1) {
+            return ValueBoolean.get(false);
+        }
+        if (rows.containsDistinct(new Value[] { l })) {
+            return ValueBoolean.get(true);
+        }
+        if (rows.containsDistinct(new Value[] { ValueNull.INSTANCE })) {
+            return ValueNull.INSTANCE;
+        }
+        return ValueBoolean.get(false);
+    }
+
+    public Value getValueSlow(LocalResult rows, Value l) {
         boolean hasNull = false;
         boolean result = all;
-        Value l = left.getValue(session);
         boolean hasRow = false;
         while (rows.next()) {
             if (!hasRow) {

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

@@ -270,7 +270,6 @@ public class LocalResult implements ResultInterface, ResultTarget {
         if (distinct) {
             if (distinctRows != null) {
                 rows = distinctRows.values();
-                distinctRows = null;
             } else {
                 if (external != null && sort != null) {
                     // external sort