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mybatis的动态sql语句很强大，在mapper映射文件中使用简单的标签即可实现该效果，下面一个个记录：
1、select查询
简单的select类似如下：
<select id="findById" resultMap="StudentResult" parameterType="Integer"> select * from t_student where id = #{id} </select>
1）if（常用于各种查询的条件判断部分）
<select id="searchStudents" parameterType="Map" resultMap="StudentResult"> select * from t_student where gradeId = #{gradeId} <if test="name != null"> and name like #{name} </if> <if test="age != null"> and age = #{age} </if> </select>
结合where标签使用如下：
<select id="searchStudents3" parameterType="Map" resultMap="StudentResult"> select * from t_student <where> <if test="gradeId != null"> gradeId = #{gradeId} </if> <if test="name != null"> and name like #{name} </if> <if test="age != null"> and age = #{age} </if> </where> </select>
2）choose（同if..else..类似）
<select id="searchStudents2" parameterType="Map" resultMap="StudentResult"> select * from t_student <choose> <when test="searchBy==‘gradeId‘"> where gradeId = #{gradeId} </when> <when test="searchBy==‘name‘"> where name like #{name} </when> <otherwise> where age = #{age} </otherwise> </choose> </select>
3）trim
<select id="searchStudents4" parameterType="Map" resultMap="StudentResult"> select * from t_student <trim prefix="where" prefixOverrides="and|or"> <if test="gradeId != null"> gradeId = #{gradeId} </if> <if test="name != null"> and name like #{name} </if> <if test="age != null"> and age = #{age} </if> </trim> </select>
prefix前置，prefixOverrides前置覆盖，简单理解为：trim子句中最前面的and或者or用where替换。
4）foreach
<select id="searchStudents5" parameterType="Map" resultMap="StudentResult"> select * from t_student <if test="gradeIds != null"> <where> gradeId in <foreach collection="gradeIds" item="gradeId" open="(" close=")" separator=","> #{gradeId} </foreach> </where> </if> </select>
collections即数组集合，可以是list类型，如arrayList等，open指定左侧拼接方式，close指定右侧，separator指定分隔符，这里拼接后为括号括起来逗号隔开的字符串，从而用于in查询。
2、update
<update id="updateStudent" parameterType="Student"> update t_student <set> <if test="name != null"> name = #{name}, </if> <if test="age != null"> age = #{age} <!-- 自动剔除最后的逗号 --> </if> </set> where id = #{id} </update>
<update id="update" parameterType="Student"> update t_student set name = #{name},age = #{age} where id = #{id} </update>
3、delete
<delete id="delete" parameterType="Integer"> delete from t_student where id = #{id} </delete>
4、insert
<!-- 插入 --> <insert id="add" parameterType="Student"> insert into t_student(id,name,age) values(null,#{name},#{age}) </insert>
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原文地址：http://www.cnblogs.com/caiya928/p/5640459.html
