improve sqlwall

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

@@ -17,7 +17,7 @@ package com.alibaba.druid.sql.ast.expr;
 
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
-public class SQLCharExpr extends SQLTextLiteralExpr {
+public class SQLCharExpr extends SQLTextLiteralExpr implements SQLValuableExpr{
 
     public SQLCharExpr(){
 
@@ -42,4 +42,9 @@ public class SQLCharExpr extends SQLTextLiteralExpr {
         visitor.visit(this);
         visitor.endVisit(this);
     }
+
+    @Override
+    public Object getValue() {
+        return this.text;
+    }
 }

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

@@ -17,7 +17,7 @@ package com.alibaba.druid.sql.ast.expr;
 
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
-public class SQLIntegerExpr extends SQLNumericLiteralExpr {
+public class SQLIntegerExpr extends SQLNumericLiteralExpr implements SQLValuableExpr{
 
     private Number number;
 
@@ -77,4 +77,9 @@ public class SQLIntegerExpr extends SQLNumericLiteralExpr {
         }
         return true;
     }
+
+    @Override
+    public Object getValue() {
+        return this.number;
+    }
 }

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

@@ -18,7 +18,9 @@ package com.alibaba.druid.sql.ast.expr;
 import com.alibaba.druid.sql.ast.SQLExprImpl;
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
-public class SQLNullExpr extends SQLExprImpl implements SQLLiteralExpr {
+import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE_NULL;
+
+public class SQLNullExpr extends SQLExprImpl implements SQLLiteralExpr, SQLValuableExpr {
 
     public SQLNullExpr(){
 
@@ -41,4 +43,9 @@ public class SQLNullExpr extends SQLExprImpl implements SQLLiteralExpr {
     public boolean equals(Object o) {
         return o instanceof SQLNullExpr;
     }
+
+    @Override
+    public Object getValue() {
+        return EVAL_VALUE_NULL;
+    }
 }

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

@@ -0,0 +1,24 @@
+/*
+ * Copyright 1999-2011 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.ast.expr;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+
+public interface SQLValuableExpr extends SQLExpr {
+
+    Object getValue();
+
+}