refactor sql parser.

src/main/java/com/alibaba/druid/sql/ast/statement/SQLUpdateStatement.java

@@ -30,6 +30,7 @@ public class SQLUpdateStatement extends SQLStatementImpl {
     protected SQLTableSource               from;
 
     protected SQLTableSource               tableSource;
+    protected List<SQLExpr>                returning;
 
     public SQLUpdateStatement(){
 
@@ -82,6 +83,14 @@ public class SQLUpdateStatement extends SQLStatementImpl {
         item.setParent(this);
     }
 
+    public List<SQLExpr> getReturning() {
+        if (returning == null) {
+            returning = new ArrayList<SQLExpr>(2);
+        }
+
+        return returning;
+    }
+
     public SQLTableSource getFrom() {
         return from;
     }