Mybatis(动态sql标签)

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.zhiyou100.hhz.dao.UsersDao">
    <!-- 动态sql片段 -->
    <sql id="userscolumn">id,name,sex,age,created</sql>
    <select id="selectByWhere" parameterType="int" resultType="com.zhiyou100.hhz.bean.Users">
        select <include refid="userscolumn"/> from users
        <!-- where 可以在第一个判断成功的语句前加where 且去除and -->
        <where>
            <if test="name!=null and name!=‘‘">
                and name=#{name}
            </if>
            <if test="sex!=null and sex!=‘‘">
                and sex=#{sex}
            </if>
            <if test="age>0">
                and age=#{age}
            </if>
        </where>
    </select>

    <update id="updateByWhere">
        update users
        <!-- set可以在第一个判断成功的语句前加set 且去除, -->
        <set>
            <if test="name!=null and name!=‘‘">
                name=#{name},
            </if>
            <if test="sex!=null and sex!=‘‘">
                sex=#{sex},
            </if>
            <if test="age>0">
                age=#{age},
            </if>
            <if test="created!=null and created!=‘‘">
                created=#{created}
            </if>
        </set>
        where id=#{id}
    </update>

    <select id="selectByWhere2" resultType="com.zhiyou100.hhz.bean.Users">
        select <include refid="userscolumn"/> from users 
        <!-- trim可以代替where和set 做到类似的效果
            prefix:添加前缀
            prefixOverrides:去除前缀
            suffix:添加后缀
            suffixOverrides:去除后缀
         -->
        <trim prefix="where" prefixOverrides="and">
            <if test="name!=null and name!=‘‘">
                and name=#{name}
            </if>
            <if test="sex!=null and sex!=‘‘">
                and sex=#{sex}
            </if>
            <if test="age>0">
                and age=#{age}
            </if>
        </trim>
    </select>

    <!-- 循环遍历数组
        collection:集合
        open:前缀
        close:后缀
        separator:每次遍历的间隔
        item:集合命名
     -->
    <delete id="deleteById">
        delete from users where id in
        <foreach collection="ids" open="(" close=")" separator="," item="id">
            #{id}
        </foreach>
    </delete>

    <select id="selectById" resultType="com.zhiyou100.hhz.bean.Users">
        select <include refid="userscolumn"/>from users 
        <where>
        <!-- choose+when+otherwise类似java中的switch+case+default -->
            <choose>
                <when test="name!=null and name!=‘‘">
                    name=#{name}
                </when>
                <when test="sex!=null and sex!=‘‘">
                    sex=#{sex}
                </when>
                <when test="age>0">
                    age=#{age}
                </when>
                <otherwise>
                    created=#{created}
                </otherwise>
            </choose>
        </where>
    </select>
</mapper>