MyBatis（4）-- 动态SQL

　　如果使用JDBC或者类似于Hibernate的其他框架，很多时候要根据需要去拼装SQL，这是一个麻烦的事情。因为某些查询需要许多条件。通常使用其他框架需要大量的Java代码进行判断，可读性比较差，而MyBatis提供对SQL语句动态的组装能力，使用XML的几个简单的元素，便能完成动态SQL的功能。大量的判断都可以在MyBatis的映射XML里面配置，以达到许多需要大量代码才能实现的功能，大大减少了代码量，这体现了MyBatis的灵活、高度可配置性和可维护性。

　　MyBatis的动态SQL包括以下几种元素：

　　

　　数据库MySQL中表：

mysql> select * from t_role;
+----+-------------+--------+
| id | role_name   | note   |
+----+-------------+--------+
|  1 | role_name_1 | note_1 |
|  2 | role_name_2 | note_2 |
|  3 | role_name_3 | note_3 |
+----+-------------+--------+
3 rows in set (0.00 sec)

　　1.if元素

　　if元素是最常见的判断语句，常常与test属性联合使用。

    <select id="findRole1" parameterType="string" resultMap="roleResultMap">
        select role_no, role_name, note from t_role where 1=1
        <if test="roleName != null and roleName !=''">
            and role_name like concat('%', #{roleName}, '%')
        </if>
    </select>

　　解决如下需求：需要根据角色名称（roleName）去查找角色，但是角色名称是一个选填条件，如果不填写，就不要用它作为条件查询。

　　当参数roleName传递进映射器时，如果参数不为空，则采取构造对roleName的模糊查询，否则就不要去构造这个条件。

　　接口：

public List<Role> findRole1(@Param("roleName") String roleName);

　　测试方法：

    public static void testFindRole1() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<Role> roleList = roleMapper.findRole1("role_name");
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　日志输出结果：

DEBUG 2018-10-08 21:07:32,127 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,375 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 1384722895.
DEBUG 2018-10-08 21:07:32,375 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,377 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role where 1=1 and role_name like concat('%', ?, '%') 
DEBUG 2018-10-08 21:07:32,400 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_name(String)
DEBUG 2018-10-08 21:07:32,424 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,425 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,425 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,426 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　2.choose、when、otherwise元素

    <select id="findRole2" parameterType="role" resultMap="roleResultMap">
        select role_no, role_name, note from t_role
        where 1=1
        <choose>
            <when test="roleNo != null and roleNo !=''">
                AND role_no = #{roleNo}
            </when>
            <when test="roleName != null and roleName !=''">
                AND role_name like concat('%', #{roleName}, '%')
            </when>
            <otherwise>
                AND note is not null
            </otherwise>
        </choose>
    </select>

　　需求：

• 如果角色编号（roleNo）不为空，则只用角色编号作为条件查询
• 当角色编号为空，而角色名称不为空时，则用角色名称作为条件进行模糊查询
• 当角色编号和角色名称都为空时，则要求角色备注不为空。

　　接口：

public List<Role> findRole2(Role role);

　　测试方法：

    public static void testFindRole2() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            Role role = new Role();
            role.setRoleNo("role_no_1");
            role.setRoleName("role_name");
            List<Role> roleList = roleMapper.findRole2(role);
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,426 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,427 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,429 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,431 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role where 1=1 AND id = ? 
DEBUG 2018-10-08 21:07:32,431 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_no_1(String)
DEBUG 2018-10-08 21:07:32,432 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 0
0
DEBUG 2018-10-08 21:07:32,432 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,432 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,432 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　3.trim、where、set元素

　　（1）使用where元素

    <select id="findRole3" parameterType="role" resultMap="roleResultMap">
        select role_no, role_name, note from t_role
        <where>
            <if test="roleName != null and roleName !=''">
                and role_name like concat('%', #{roleName}, '%')
            </if>
            <if test="note != null and note !=''">
                and note like concat('%', #{note}, '%')
            </if>
        </where>
    </select>

　　对比于上面的choose、when和otherwise元素，使用where元素可以去掉条件“1=1”。当where元素里面的条件成立时，才会加入where这个SQL关键字到组装的SQL里面，否则就不加入。

　　接口：

public List<Role> findRole3(Role role);

　　测试方法：

    public static void testFindRole3() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            Role role = new Role();
            role.setRoleNo("role_no_1");
            role.setRoleName("role_name");
            List<Role> roleList = roleMapper.findRole3(role);
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,433 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,433 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,433 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,434 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role WHERE role_name like concat('%', ?, '%') 
DEBUG 2018-10-08 21:07:32,434 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_name(String)
DEBUG 2018-10-08 21:07:32,436 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,436 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,436 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,437 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　（2）使用trim元素

    <select id="findRole4" parameterType="string" resultMap="roleResultMap">
        select role_no, role_name, note from t_role
        <trim prefix="where" prefixOverrides="and">
            <if test="roleName != null and roleName !=''">
                and role_name like concat('%', #{roleName}, '%')
            </if>
        </trim>
    </select>

　　trim元素意味着要去掉一些特殊的字符串，prefix代表的是语句的前缀，而prefixOverrides代表的是需要去掉哪种字符串，上面的写法基本与where是等效的。

　　即如果and成立，就使用where条件；否则，不使用where条件与and条件。

　　接口：

public List<Role> findRole4(@Param("roleName") String roleName);

　　测试方法：

    public static void testFindRole4() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<Role> roleList = roleMapper.findRole4("role_name");
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,437 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,437 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,439 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,439 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role where role_name like concat('%', ?, '%') 
DEBUG 2018-10-08 21:07:32,439 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_name(String)
DEBUG 2018-10-08 21:07:32,440 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,440 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,441 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,441 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　（3）使用set元素

    <update id="updateRole" parameterType="role">
        update t_role
        <set>
            <if test="roleName != null and roleName !=''">
                role_name = #{roleName},
            </if>
            <if test="note != null and note != ''">
                note = #{note}
            </if>
        </set>
        where id = #{roleNo}
    </update>

　　set元素遇到了逗号，它会把对应的逗号去掉。这样当只想更新备注时，只需要传递备注信息和角色编号即可，而不需要再传递角色名称。MyBatis就会根据参数的规则进行动态SQL组装，这样便能满足要求，而避免全部字段更新的问题。

　　接口：

public int updateRole(Role role);

　　测试方法：

    public static void testUpdateRole() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            Role role = new Role();
            role.setNote("note_1_update");
            role.setRoleName("role_name_1_update");
            role.setRoleNo("role_no_1");
            int result = roleMapper.updateRole(role);
            System.out.println(result);
            sqlSession.commit();
        } catch(Exception ex) {
            sqlSession.rollback();
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,449 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,449 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,450 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,450 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: update t_role SET role_name = ?, note = ? where id = ? 
DEBUG 2018-10-08 21:07:32,450 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_name_1_update(String), note_1_update(String), role_no_1(String)
DEBUG 2018-10-08 21:07:32,451 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==    Updates: 0
0
DEBUG 2018-10-08 21:07:32,452 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,452 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,452 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,452 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　4.foreach元素

    <select id="findRoleByNums" resultMap="roleResultMap">
        select id, role_name, note from t_role where id in
        <foreach item="roleNo" index="index" collection="roleNoList"
            open="(" separator="," close=")">
            #{roleNo}
        </foreach>
    </select>

　　foreach元素是一个循环语句，它的作用是遍历集合，能够很好地支持数组和List、Set接口的集合，对此提供遍历功能。往往用于SQL中的in关键字。

• collection配置的roleNoList是传递进来的参数名称，它可以是一个数组、List、Set等集合
• item配置的是当前元素在集合的位置下标
• index配置的是当前元素在集合的位置下标
• open和close配置的是以什么符号将这些集合元素包装起来
• separator是各个元素的间隔符

　　接口：

public List<Role> findRoleByNums(@Param("roleNoList") List<String> roleNoList);

　　测试方法：

    public static void testFindRoleByNums() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<String> roleNoList = new ArrayList<String>();
            roleNoList.add("role_no_1");
            roleNoList.add("role_no_2");
            roleNoList.add("role_no_3");
            List<Role> roleList = roleMapper.findRoleByNums(roleNoList);
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,454 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,454 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,455 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,455 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role where id in ( ? , ? , ? ) 
DEBUG 2018-10-08 21:07:32,456 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: role_no_1(String), role_no_2(String), role_no_3(String)
DEBUG 2018-10-08 21:07:32,456 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 0
0
DEBUG 2018-10-08 21:07:32,457 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,457 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,457 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　5.用test的属性判断字符串

    <select id="getRoleTest" parameterType="string" resultMap="roleResultMap">
        select id, role_name, note from t_role
        <if test="type == 'Y'.toString()">
            where 1=1
        </if>
    </select>

　　如果把type=“Y”传递给SQL，就可以发现MyBatis加入了条件where 1=1。

　　对于字符串的判断，可以通过加入toString()方法进行比较。

　　接口：

public List<Role> getRoleTest(@Param("type") String type);

　　测试方法：

    public static void testGetRoleTest() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<Role> roleList = roleMapper.getRoleTest("Y");
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,461 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,461 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,461 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,462 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select id, role_name, note from t_role where 1=1 
DEBUG 2018-10-08 21:07:32,462 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 
DEBUG 2018-10-08 21:07:32,464 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,464 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,464 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,464 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　6.bind元素

　　bind元素的作用是通过OGNL表达式去自定义一个上下文变量，这样更方便使用。

　　（1）使用bind元素绑定单个参数

    <select id="findRole5" parameterType="string" resultMap="roleResultMap">
        <bind name="pattern" value="'%' + _parameter + '%'" />
        SELECT id, role_name, note FROM t_role
        where role_name like #{pattern}
    </select>

　　“_parameter”表示传递进来的参数，它和通配符（%）连接后赋给了pattren变量，然后就可以在select语句中使用这个变量进行模糊查询了。

　　接口：

public List<Role> findRole5(String roleName);

　　测试方法：

    public static void testFindRole5() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<Role> roleList = roleMapper.findRole5("role_name");
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,443 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,444 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,444 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,444 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: SELECT id, role_name, note FROM t_role where role_name like ? 
DEBUG 2018-10-08 21:07:32,444 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: %role_name%(String)
DEBUG 2018-10-08 21:07:32,446 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,446 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,446 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,446 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.

　　（2）使用bind元素绑定多个参数

    <select id="findRole6" resultMap="roleResultMap">
        <bind name="pattern_roleName" value="'%' + roleName + '%'" />
        <bind name="pattern_note" value="'%' + note + '%'" />
        SELECT id, role_name, note FROM t_role
        where role_name like
        #{pattern_roleName}
        and note like #{pattern_note}
    </select>

　　这里绑定了两个新的变量pattern_roleName和pattern_note，然后就可以在SQL的其他地方使用了，如进行模糊查询。

　　接口：

public List<Role> findRole6(@Param("roleName") String roleName, @Param("note") String note);

　　测试方法：

    public static void testFindRole6() {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
            List<Role> roleList = roleMapper.findRole6("role_name", "note");
            System.out.println(roleList.size());
        } catch(Exception ex) {
            ex.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

　　结果：

DEBUG 2018-10-08 21:07:32,447 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
DEBUG 2018-10-08 21:07:32,447 org.apache.ibatis.datasource.pooled.PooledDataSource: Checked out connection 1384722895 from pool.
DEBUG 2018-10-08 21:07:32,447 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,447 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: SELECT id, role_name, note FROM t_role where role_name like ? and note like ? 
DEBUG 2018-10-08 21:07:32,448 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: %role_name%(String), %note%(String)
DEBUG 2018-10-08 21:07:32,448 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 3
3
DEBUG 2018-10-08 21:07:32,449 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,449 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@528931cf]
DEBUG 2018-10-08 21:07:32,449 org.apache.ibatis.datasource.pooled.PooledDataSource: Returned connection 1384722895 to pool.