MyBatis实现动态SQL的方法

<resultMap id="employeeMap" type="com.dao.Employee">
    <id property="empId" column="employee_id"/>
    <result property="empName" column="employee_name"/>
    <result property="empAge" column="employee_age"/>
    <result property="empSex" column="employee_sex"/>
    <result property="empEmail" column="employee_email"/>
    <result property="empAddress" column="employee_address"/>
</resultMap>

<select id="getEmpIf" parameterType="com.dao.Employee" resultMap="employeeMap">
    select * from employee where
    <if test="empName != null and empName != ''">
        employee_name=#{empName}
    </if>
</select>

<select id="getEmpWhereIf" parameterType="com.dao.Employee" resultMap="employeeMap">
    select * from employee
    <where>
        <if test="empName != null and empName !=''">
            and employee_name=#{empName}
        </if>
    </where>
</select>

<update id="UpdateEmployee" parameterType="com.dao.Employee">
    update employee
    <set>
        <if test="empName != null and empName !=''">
            employee_name=#{empName},
        </if>
    </set>
    where employee_id=#{empId}
</update>

<select id="getEmpWhereIf" parameterType="com.dao.Employee" resultMap="employeeMap">
    select * from employee
    <!-- 添加前缀 where，移除 and 或 or -->
    <trim prefix="where" prefixOverrides="and | or">
        <if test="empName != null">
            and employee_name=#{empName}
        </if>
    </trim>
</select>

<select id="selectEmployeeByChoose" resultType="com.dao.Employee" parameterMap="employeeMap">
    select * from employee
    <where>
        <choose>
            <when test="empName!= null and empName!=''">
                employee_name=#{empName}
            </when>
            <when test="empAddress!= null and empAddress!=''">
                and employee_address=#{empAddress}
            </when>
            <otherwise>
                and employee_age=#{empAge}
            </otherwise>
        </choose>
    </where>
</select>

在 Mapper.xml SQL 映射文件
<select id="selectEmployeeByListId" resultMap="employeeMap">
    select * from employee
    <where>
        <!-- where employee_id in (?,?,?,?)-->
<!--        <foreach collection="ids" item="id" open="employee_id in (" close=")" separator=",">-->
<!--            #{id}-->
<!--        </foreach>-->
        <!-- where employee_id=? or employee_id=?... -->
        <foreach collection="ids" item="id" separator="or">
            employee_id=#{id}
        </foreach>
    </where>
</select>

在 Mapper.java 接口
List<Employee> selectEmployeeByListId(@Param("ids") List<Integer> ids);

在 Test 测试类
@Test
public void testSelectByListid() {
    List<Integer> ids = new ArrayList<>();
    ids.add(1);
    ids.add(2);
    ids.add(4);
    ids.add(5);
    List<Employee> employees = mapper.selectEmployeeByListId(ids);
    for (Employee employee : employees) {
        System.out.println(employee);
    }
}

<!-- 查询姓马的员工 -->
<select id="selectEmployeeByName" parameterType="com.dao.Employee" resultMap="employeeMap">
    <bind name="pattern" value="'%' + empName + '%'"/>
    select * from employee where employee_name like #{pattern}
</select>