修改评论模型：因为pid为外键，修改pid默认为null

DataModelDiagram/zheng.pdb

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<?PowerDesigner AppLocale="UTF16" ID="{22E867D0-73E2-4C77-BB68-28135519D681}" Label="" LastModificationDate="1479649194" Name="zheng" Objects="196" Symbols="34" Target="MySQL 5.0" Type="{CDE44E21-9669-11D1-9914-006097355D9B}" signature="PDM_DATA_MODEL_XML" version="16.5.0.3982"?>
+<?PowerDesigner AppLocale="UTF16" ID="{22E867D0-73E2-4C77-BB68-28135519D681}" Label="" LastModificationDate="1479651239" Name="zheng" Objects="196" Symbols="43" Target="MySQL 5.0" Type="{CDE44E21-9669-11D1-9914-006097355D9B}" signature="PDM_DATA_MODEL_XML" version="16.5.0.3982"?>
 <!-- do not edit this file -->
 
 <Model xmlns:a="attribute" xmlns:c="collection" xmlns:o="object">
@@ -5484,7 +5484,7 @@ LABL 0 新宋体,8,N</a:FontList>
 <a:Code>cms_comment</a:Code>
 <a:CreationDate>1478091704</a:CreationDate>
 <a:Creator>shuzheng</a:Creator>
-<a:ModificationDate>1479631642</a:ModificationDate>
+<a:ModificationDate>1479650437</a:ModificationDate>
 <a:Modifier>shuzheng</a:Modifier>
 <a:PhysicalOptions>ENGINE=InnoDB DEFAULT CHARSET=utf8mb4</a:PhysicalOptions>
 <a:TotalSavingCurrency/>
@@ -5512,10 +5512,10 @@ LABL 0 新宋体,8,N</a:FontList>
 <a:Code>pid</a:Code>
 <a:CreationDate>1478091704</a:CreationDate>
 <a:Creator>shuzheng</a:Creator>
-<a:ModificationDate>1479649194</a:ModificationDate>
+<a:ModificationDate>1479651239</a:ModificationDate>
 <a:Modifier>shuzheng</a:Modifier>
 <a:Comment>回复楼中楼编号回复楼中楼编号</a:Comment>
-<a:DefaultValue>0</a:DefaultValue>
+<a:DefaultValue>NULL</a:DefaultValue>
 <a:DataType>int(10)</a:DataType>
 <a:Length>10</a:Length>
 <a:ExtendedAttributesText>{F4F16ECD-F2F1-4006-AF6F-638D5C65F35E},MYSQL50,56={4A2BD2F3-4A8A-4421-8A48-A8029BDA28E8},Unsigned,4=true
@@ -5989,10 +5989,11 @@ LABL 0 新宋体,8,N</a:FontList>
 <a:Code>Reference_2</a:Code>
 <a:CreationDate>1478091704</a:CreationDate>
 <a:Creator>shuzheng</a:Creator>
-<a:ModificationDate>1479631642</a:ModificationDate>
+<a:ModificationDate>1479650437</a:ModificationDate>
 <a:Modifier>shuzheng</a:Modifier>
 <a:Cardinality>0..*</a:Cardinality>
-<a:DeleteConstraint>3</a:DeleteConstraint>
+<a:UpdateConstraint>2</a:UpdateConstraint>
+<a:DeleteConstraint>2</a:DeleteConstraint>
 <c:ParentTable>
 <o:Table Ref="o41"/>
 </c:ParentTable>

DataModelDiagram/zheng.pdm

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<?PowerDesigner AppLocale="UTF16" ID="{22E867D0-73E2-4C77-BB68-28135519D681}" Label="" LastModificationDate="1479650437" Name="zheng" Objects="196" Symbols="40" Target="MySQL 5.0" Type="{CDE44E21-9669-11D1-9914-006097355D9B}" signature="PDM_DATA_MODEL_XML" version="16.5.0.3982"?>
+<?PowerDesigner AppLocale="UTF16" ID="{22E867D0-73E2-4C77-BB68-28135519D681}" Label="" LastModificationDate="1479651239" Name="zheng" Objects="196" Symbols="43" Target="MySQL 5.0" Type="{CDE44E21-9669-11D1-9914-006097355D9B}" signature="PDM_DATA_MODEL_XML" version="16.5.0.3982"?>
 <!-- do not edit this file -->
 
 <Model xmlns:a="attribute" xmlns:c="collection" xmlns:o="object">
@@ -5512,10 +5512,10 @@ LABL 0 新宋体,8,N</a:FontList>
 <a:Code>pid</a:Code>
 <a:CreationDate>1478091704</a:CreationDate>
 <a:Creator>shuzheng</a:Creator>
-<a:ModificationDate>1479649194</a:ModificationDate>
+<a:ModificationDate>1479651239</a:ModificationDate>
 <a:Modifier>shuzheng</a:Modifier>
 <a:Comment>回复楼中楼编号回复楼中楼编号</a:Comment>
-<a:DefaultValue>0</a:DefaultValue>
+<a:DefaultValue>NULL</a:DefaultValue>
 <a:DataType>int(10)</a:DataType>
 <a:Length>10</a:Length>
 <a:ExtendedAttributesText>{F4F16ECD-F2F1-4006-AF6F-638D5C65F35E},MYSQL50,56={4A2BD2F3-4A8A-4421-8A48-A8029BDA28E8},Unsigned,4=true

DataModelDiagram/zheng.sql

@@ -1,6 +1,6 @@
 /*==============================================================*/
 /* DBMS name:      MySQL 5.0                                    */
-/* Created on:     2016/11/20 22:00:49                          */
+/* Created on:     2016/11/20 22:14:12                          */
 /*==============================================================*/
 
 
@@ -128,7 +128,7 @@ alter table cms_category_tag comment 'cms_category_tag 类目标签关联表';
 create table cms_comment
 (
    comment_id           int(10) unsigned not null auto_increment comment '编号',
-   pid                  int(10) unsigned default 0 comment '回复楼中楼编号回复楼中楼编号',
+   pid                  int(10) unsigned default NULL comment '回复楼中楼编号回复楼中楼编号',
    article_id           int(10) unsigned not null comment '文章编号',
    user_id              int(10) unsigned not null comment '用户编号',
    content              text not null comment '评论内容',