improve wall filter

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

@@ -37,6 +37,9 @@ public class SQLExprTableSource extends SQLTableSourceImpl {
     }
 
     public void setExpr(SQLExpr expr) {
+        if (expr != null) {
+            expr.setParent(this);
+        }
         this.expr = expr;
     }
 

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

@@ -32,7 +32,7 @@ public class SQLSelect extends SQLObjectImpl {
     }
     
     public SQLSelect(SQLSelectQuery query) {
-        this.query = query;
+        this.setQuery(query);
     }
 
     public SQLWithSubqueryClause getWithSubQuery() {
@@ -48,6 +48,9 @@ public class SQLSelect extends SQLObjectImpl {
     }
 
     public void setQuery(SQLSelectQuery query) {
+        if (query != null) {
+            query.setParent(this);
+        }
         this.query = query;
     }
 

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

@@ -33,12 +33,11 @@ public class SQLSubqueryTableSource extends SQLTableSourceImpl {
 
     public SQLSubqueryTableSource(SQLSelect select, String alias){
         super(alias);
-        this.select = select;
+        this.setSelect(select);
     }
 
     public SQLSubqueryTableSource(SQLSelect select){
-
-        this.select = select;
+        this.setSelect(select);
     }
 
     public SQLSelect getSelect() {
@@ -46,6 +45,9 @@ public class SQLSubqueryTableSource extends SQLTableSourceImpl {
     }
 
     public void setSelect(SQLSelect select) {
+        if (select != null) {
+            select.setParent(this);
+        }
         this.select = select;
     }
 

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

@@ -44,6 +44,9 @@ public class SQLUnionQuery extends SQLSelectQuery {
     }
 
     public void setLeft(SQLSelectQuery left) {
+        if (left != null) {
+            left.setParent(this);
+        }
         this.left = left;
     }
 
@@ -52,6 +55,9 @@ public class SQLUnionQuery extends SQLSelectQuery {
     }
 
     public void setRight(SQLSelectQuery right) {
+        if (right != null) {
+            right.setParent(this);
+        }
         this.right = right;
     }
 
@@ -60,6 +66,9 @@ public class SQLUnionQuery extends SQLSelectQuery {
     }
 
     public void setOrderBy(SQLOrderBy orderBy) {
+        if (orderBy != null) {
+            orderBy.setParent(this);
+        }
         this.orderBy = orderBy;
     }