improved sql parser.

src/main/java/com/alibaba/druid/sql/ast/expr/SQLBinaryOpExpr.java

@@ -289,4 +289,12 @@ public class SQLBinaryOpExpr extends SQLExprImpl implements Serializable {
 
         return new SQLBinaryOpExpr(a, SQLBinaryOperator.BooleanAnd, b);
     }
+
+    public static SQLBinaryOpExpr isNotNull(SQLExpr expr) {
+        return new SQLBinaryOpExpr(expr, SQLBinaryOperator.IsNot, new SQLNullExpr());
+    }
+
+    public static SQLBinaryOpExpr isNull(SQLExpr expr) {
+        return new SQLBinaryOpExpr(expr, SQLBinaryOperator.Is, new SQLNullExpr());
+    }
 }

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

@@ -18,5 +18,7 @@ package com.alibaba.druid.sql.ast.statement;
 import com.alibaba.druid.sql.ast.SQLObject;
 
 public interface SQLSelectQuery extends SQLObject {
+    boolean isBracket();
+    void setBracket(boolean bracket);
 
 }

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

@@ -25,7 +25,7 @@ import com.alibaba.druid.sql.ast.SQLOrderBy;
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
 public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery {
-
+    private boolean                     bracket         = false;
     protected int                       distionOption;
     protected final List<SQLSelectItem> selectList      = new ArrayList<SQLSelectItem>();
 
@@ -376,4 +376,14 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
             x.setLimit(limit.clone());
         }
     }
+
+    @Override
+    public boolean isBracket() {
+        return bracket;
+    }
+
+    @Override
+    public void setBracket(boolean bracket) {
+        this.bracket = bracket;
+    }
 }

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

@@ -22,6 +22,8 @@ import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
 public class SQLUnionQuery extends SQLObjectImpl implements SQLSelectQuery {
 
+    private boolean          bracket  = false;
+
     private SQLSelectQuery   left;
     private SQLSelectQuery   right;
     private SQLUnionOperator operator = SQLUnionOperator.UNION;
@@ -96,4 +98,12 @@ public class SQLUnionQuery extends SQLObjectImpl implements SQLSelectQuery {
         }
         this.limit = limit;
     }
+
+    public boolean isBracket() {
+        return bracket;
+    }
+
+    public void setBracket(boolean bracket) {
+        this.bracket = bracket;
+    }
 }