SQL Server: if possible, use OFFSET and FETCH instead of JDBC methods (…

…#300)

Signed-off-by: Richard DiCroce <Rich.DiCroce@scientificgames.com>

foundation/org.eclipse.persistence.core/src/org/eclipse/persistence/platform/database/SQLServerPlatform.java

@@ -45,8 +45,8 @@
  * @since TOPLink/Java 1.0
  */
 public class SQLServerPlatform extends org.eclipse.persistence.platform.database.DatabasePlatform {
-    /** Support for sequence objects added in SQL Server 2012 */
-    private boolean supportsSequenceObjects;
+    /** Support for sequence objects and OFFSET FETCH NEXT added in SQL Server 2012 */
+    private boolean isVersion11OrHigher;
     private boolean isConnectionDataInitialized;
 
     public SQLServerPlatform(){
@@ -62,7 +62,7 @@ public void initializeConnectionData(Connection connection) throws SQLException
         }
         DatabaseMetaData dmd = connection.getMetaData();
         int databaseVersion = dmd.getDatabaseMajorVersion();
-        supportsSequenceObjects = databaseVersion >= 11;
+        isVersion11OrHigher = databaseVersion >= 11;
         isConnectionDataInitialized = true;
         this.driverSupportsNationalCharacterVarying = Helper.compareVersions(dmd.getDriverVersion(), "4.0.0") >= 0;
     }
@@ -690,7 +690,7 @@ public boolean supportsIdentity() {
      */
     @Override
     public boolean supportsSequenceObjects() {
-        return supportsSequenceObjects;
+        return isVersion11OrHigher;
     }
 
     /**
@@ -732,4 +732,47 @@ public void writeUpdateOriginalFromTempTableSql(Writer writer, DatabaseTable tab
         writer.write(tempTableName);
         writeAutoJoinWhereClause(writer, tableName, tempTableName, pkFields, this);
     }
+
+    @Override
+    public void printSQLSelectStatement(DatabaseCall call, ExpressionSQLPrinter printer, SQLSelectStatement statement) {
+        ReadQuery query = statement.getQuery();
+        if (query == null || !isVersion11OrHigher || !shouldUseRownumFiltering()) {
+            super.printSQLSelectStatement(call, printer, statement);
+            return;
+        }
+
+        int max = Math.max(0, query.getMaxRows());
+        int first = Math.max(0, query.getFirstResult());
+
+        if (max == 0 && first == 0) {
+            super.printSQLSelectStatement(call, printer, statement);
+            return;
+        }
+
+        // OFFSET + FETCH NEXT requires ORDER BY, so add an ordering if there are none
+        // this SQL will satisfy the query parser without actually changing the ordering of the rows
+        List<Expression> orderBy = statement.getOrderByExpressions();
+        if (orderBy.isEmpty()) {
+            orderBy.add(statement.getBuilder().literal("ROW_NUMBER() OVER (ORDER BY (SELECT null))"));
+        }
+
+        // decide exact syntax to use, depending on whether a limit is specified (could just have an offset)
+        String offsetFetchSql;
+        List<?> offsetFetchArgs;
+        if (max == 0) {
+            offsetFetchSql = "? OFFSET ? ROWS";
+            offsetFetchArgs = Arrays.asList(first);
+        } else {
+            offsetFetchSql = "? OFFSET ? ROWS FETCH NEXT ? ROWS ONLY";
+            offsetFetchArgs = Arrays.asList(first, max - first);
+        }
+
+        // append to the last ORDER BY clause
+        orderBy.add(orderBy.remove(orderBy.size() - 1).sql(offsetFetchSql, offsetFetchArgs));
+
+        super.printSQLSelectStatement(call, printer, statement);
+
+        call.setIgnoreFirstRowSetting(true);
+        call.setIgnoreMaxResultsSetting(true);
+    }
 }