new feature : sql builder

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

@@ -27,7 +27,12 @@ public class SQLExprTableSource extends SQLTableSourceImpl {
     }
 
     public SQLExprTableSource(SQLExpr expr){
+        this(expr, null);
+    }
+    
+    public SQLExprTableSource(SQLExpr expr, String alias){
         this.setExpr(expr);
+        this.setAlias(alias);
     }
 
     public SQLExpr getExpr() {

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

@@ -82,6 +82,11 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
     public List<SQLSelectItem> getSelectList() {
         return this.selectList;
     }
+    
+    public void addSelectItem(SQLSelectItem item) {
+        this.selectList.add(item);
+        item.setParent(this);
+    }
 
     public SQLTableSource getFrom() {
         return this.from;

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

@@ -75,6 +75,11 @@ public class SQLUpdateStatement extends SQLStatementImpl {
     public List<SQLUpdateSetItem> getItems() {
         return items;
     }
+    
+    public void addItem(SQLUpdateSetItem item) {
+        this.items.add(item);
+        item.setParent(this);
+    }
 
     @Override
     public void output(StringBuffer buf) {