Mybatis 动态 SQL - script，bind，多数据库支持

script

在使用注解的映射器类中使用动态SQL时，可以使用`<script>`元素。例如：

 @Update({"<script>","update Author","  <set>","    <if test='username != null'>username=#{username},</if>","    <if test='password != null'>password=#{password},</if>","    <if test='email != null'>email=#{email},</if>","    <if test='bio != null'>bio=#{bio}</if>","  </set>","where id=#{id}","</script>"})void updateAuthorValues(Author author);

 bind

`<bind>`元素允许您将一个OGNL表达式的结果绑定到上下文中创建的变量上。例如：

<select id="selectBlogsLike" resultType="Blog"><bind name="pattern" value="'%' + _parameter.getTitle() + '%'" />SELECT * FROM BLOGWHERE title LIKE #{pattern}
</select>

 多数据库支持

如果配置了`databaseIdProvider`，则可以在动态代码中使用一个名为`_databaseId`的变量，以此来根据数据库供应商构建不同的语句。请看下面的示例：

<insert id="insert"><selectKey keyProperty="id" resultType="int" order="BEFORE"><if test="_databaseId == 'oracle'">select seq_users.nextval from dual</if><if test="_databaseId == 'db2'">select nextval for seq_users from sysibm.sysdummy1"</if></selectKey>insert into users values (#{id}, #{name})
</insert>