improve sql parser

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

@@ -27,7 +27,7 @@ public class SQLAlterTableAddForeignKey extends SQLObjectImpl implements SQLAlte
     }
 
     public SQLAlterTableAddForeignKey(SQLForeignKeyConstraint foreignKey){
-        this.foreignKey = foreignKey;
+       this.setForeignKey(foreignKey);
     }
 
     public SQLForeignKeyConstraint getForeignKey() {
@@ -35,6 +35,9 @@ public class SQLAlterTableAddForeignKey extends SQLObjectImpl implements SQLAlte
     }
 
     public void setForeignKey(SQLForeignKeyConstraint foreignKey) {
+        if (foreignKey != null) {
+            foreignKey.setParent(this);
+        }
         this.foreignKey = foreignKey;
     }
 

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

@@ -0,0 +1,53 @@
+/*
+ * 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.statement;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.alibaba.druid.sql.ast.SQLName;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+public class SQLColumnReference extends SQLConstaintImpl implements SQLColumnConstraint {
+
+    private SQLName       table;
+    private List<SQLName> columns = new ArrayList<SQLName>();
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, this.getName());
+        }
+        visitor.endVisit(this);
+    }
+
+    public SQLName getTable() {
+        return table;
+    }
+
+    public void setTable(SQLName table) {
+        this.table = table;
+    }
+
+    public List<SQLName> getColumns() {
+        return columns;
+    }
+
+    public void setColumns(List<SQLName> columns) {
+        this.columns = columns;
+    }
+
+}

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

@@ -0,0 +1,30 @@
+/*
+ * 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.statement;
+
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+public class SQLColumnUniqueKey extends SQLConstaintImpl implements SQLColumnConstraint {
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, this.getName());
+        }
+        visitor.endVisit(this);
+    }
+
+}

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

@@ -19,13 +19,18 @@ import java.util.ArrayList;
 import java.util.List;
 
 import com.alibaba.druid.sql.ast.SQLName;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 
-public abstract class SQLForeignKeyImpl extends SQLConstaintImpl implements SQLForeignKeyConstraint {
+public class SQLForeignKeyImpl extends SQLConstaintImpl implements SQLForeignKeyConstraint {
 
     private SQLName       referencedTableName;
     private List<SQLName> referencingColumns = new ArrayList<SQLName>();
     private List<SQLName> referencedColumns  = new ArrayList<SQLName>();
 
+    public SQLForeignKeyImpl(){
+
+    }
+
     @Override
     public List<SQLName> getReferencingColumns() {
         return referencingColumns;
@@ -46,4 +51,15 @@ public abstract class SQLForeignKeyImpl extends SQLConstaintImpl implements SQLF
         return referencedColumns;
     }
 
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, this.getName());
+            acceptChild(visitor, this.getReferencedTableName());
+            acceptChild(visitor, this.getReferencingColumns());
+            acceptChild(visitor, this.getReferencedColumns());
+        }
+        visitor.endVisit(this);        
+    }
+
 }