有些是预先生成(pre-generate)主键的，如Oracle和PostgreSQL；有些是事后生成(post-generate)主键的，如MySQL和SQL Server。但是不管是哪种方式，我们都可以用iBATIS的节点来获取语句所产生的主键。
         
    例子如下：

xml 代码
 
<insert id="insertProduct-ORACLE" parameterClass="product">
  <selectKey resultClass="int" type="pre" keyProperty="Id" >
     SELECT YOURPKSEQUENCE.NEXTVAL AS VALUE FROM DUAL
  <selectKey>
  insert into PRODUCT (PRD_ID,PRD_DESCRIPTION) values (#id#,#description#)
<insert>

<insert id="insertProduct-MS-SQL" parameterClass="product">
  insert into PRODUCT (PRD_DESCRIPTION) values (#description#)
  <selectKey resultClass="int" type="post" keyProperty="id" >
    select @@IDENTITY as value
  <selectKey>
<insert>

<insert id="insertProduct-MYSQL" parameterClass="product">
  insert into PRODUCT (PRD_DESCRIPTION) values (#description#)
  <selectKey resultClass="int" type="post" keyProperty="id" >
    select LAST_INSERT_ID() as value
  <selectKey>
<insert>