iBatis自动生成的主键　返回主键 (Oracle,Sql Server,Mysql,SQLite)

iBatis自动生成的主键

很多数据库支持自动生成主键的数据类型。不过这通常（并不总是）是个私有的特性。
SQL Map 通过<insert>的子元素<selectKey>来支持自动生成的键值。它同时支持预生成（如
Oracle）和后生成两种类型（如 MS-SQL Server）。下面是两个例子：

< !—Oracle SEQUENCE Example -->

<insert id="insertProduct-ORACLE" parameterClass="com.domain.Product">  
  insert into PRODUCT (PRD_ID,PRD_DESCRIPTION) 
  values (#id#,#description#)
  <selectKey resultClass="int" keyProperty="id">
    SELECT STOCKIDSEQUENCE.NEXTVAL AS ID FROM DUAL
  </selectKey>
</insert> 

<!— Microsoft SQL Server IDENTITY Column Example -->

<insert id="insertProduct-MS-SQL" parameterClass="com.domain.Product"> 
  insert into PRODUCT (PRD_DESCRIPTION) 
  values (#description#) 
  <selectKey resultClass="int" keyProperty="id" > 
    SELECT @@IDENTITY AS ID 
  </selectKey> 
</insert>

<!-- Mysql Auto Increased ID-->

<insert id="insertProduct-Mysql" parameterClass="com.domain.Product">
  insert into PRODUCT(PRD_DESCRIPTION)
  values (#description#)
  <selectKey resultClass="int" keyProperty="id">
    SELECT LAST_INSERT_ID()
  </selectKey>
</insert>

<!-- SQLite-->

<insert id="Create" parameterClass="Subject">
      INSERT INTO SUBJECT
      (SubjectName,QuestionCount,IsNowPaper)
      VALUES(#SubjectName#,#QuestionCount#,#IsNowPaper#)
      <selectKey resultClass="int" type="post" property="SubjectId">
        SELECT seq
        FROM sqlite_sequence
        WHERE (name = 'SUBJECT')
      </selectKey>
</insert>

注意：name = 'SUBJECT'中SUBJECT为表名称