mybatis中bind的使用示例详解

<bind name="变量名" value="OGNL表达式"/>

<select id="searchUsers" resultType="User">
    <bind name="pattern" value="'%' + username + '%'"/>
    SELECT * FROM users 
    WHERE username LIKE #{pattern}
</select>

<select id="getUsers" resultType="User">
    <bind name="filterName" value="name != null ? name : '%'"/>
    SELECT * FROM users
    WHERE name LIKE #{filterName}
</select>

<select id="calculate" resultType="double">
    <bind name="total" value="price * quantity"/>
    <bind name="discounted" value="total * (1 - discount)"/>
    SELECT #{discounted} AS final_price
</select>

<select id="pageListUser" resultType="com.demo.entity.User"
            parameterType="java.util.List">
    select * from user 
    where name = #{name}
    <if test="pageNo != null and pageSize != null">
        <bind name="pageNo" value="(pageNo-1)*pageSize"/>
        limit #{pageNo},#{pageSize}
    </if>
</select>

<select id="getUsersByNameAndAge" resultType="User">
    SELECT * FROM users
    WHERE name = #{name} AND age >= <bind name="minAge" value="${minAge}" />
</select>

select * from(
	select * from user where name='张三' order by id
) t0
union all
select * from(
	select * from user where name='李四' order by id
) t1

@Autowired
private UserMapper userMapper;
public List<User> selectByNameList(){
    userMapper.selectByNameList(Arrays.asList("张三","李四"));
    return null;
}

public interface UserMapper  {
    List<User> selectByNameList(List<String> nameList);
}

<select id="selectByNameList" resultType="com.demo.entity.User"
            parameterType="java.util.List">
    <foreach collection="list" item="item" separator="union all"  index="index">
        select * from (
            select * from user where name = #{item} order by id
        ) t#{index}
    </foreach>
</select>

==>  Preparing: select * from ( select * from user where name = ? order by id ) t? union all select * from ( select * from user where name = ? order by id ) t?
==> Parameters: 张三(String), 0(Integer), 李四(String), 1(Integer)

<select id="selectByNameList" resultType="com.demo.entity.User"
            parameterType="java.util.List">
    <foreach collection="list" item="item" separator="union all"  index="index">
        <bind name="tableName" value="'t' + index"></bind>
        select * from (
            select * from user where name = #{item} order by id
        ) ${tableName}
    </foreach>
</select>

==>  Preparing: select * from ( select * from user where name = ? order by id ) t0 union all select * from ( select * from user where name = ? order by id ) t1
==> Parameters: 张三(String), 李四(String)

<select id="selectByNameList" resultType="com.demo.entity.User"
            parameterType="java.util.List">
    <foreach collection="list" item="item" separator="union all"  index="index">
        <bind name="tableName" value="'t' + index"></bind>
        select * from (
            select * from user where name = #{item} order by id
        ) #{tableName}
    </foreach>
</select>

==>  Preparing: select * from ( select * from user where name = ? order by id ) ? union all select * from ( select * from user where name = ? order by id ) ?
==> Parameters: 张三(String), t1(String), 李四(String), t1(String)

<foreach item="item" collection="list" separator=",">
  <!-- 错误：每次循环覆盖 previousItem，最终所有值相同 -->
  <bind name="previousItem" value="item" />
  #{previousItem}
</foreach>