MyBatis第四天

一丶动态SQL【重点】

1.1《SQL》

<sql id="BBBB">
            SELECT * FROM empmanager
        </sql>
        <select id="selsectId" resultType="Empmanager">
            <include refid="BBBB"></include>
            where username = #{age0}
        </select>

1.2《IF》

    <select id="selsectId" resultType="Empmanager">
        <include refid="BBBB"></include>
        where
        <if test="name!=null">
            name = #{name}
        </if>
        <if test="id!=null">
            id = #{id}
        </if>
    </select>

1.3《WHERE》

where标签：会识别以or或and 会自动去除

    <select id="selsectId" resultType="Empmanager">
        <include refid="BBBB"></include>
        <where>
            <if test="name!=null">
                name = #{name}
            </if>
            <if test="id!=null">
                and id = #{id}
            </if>
        </where>
    </select>

1.4《SET》

<set>满足条件的if语句   set标签：会自动忽略后戳（，）
    <if test="name!=null>
        name = #{name},
    </if>
    <if test="sort!=null>
        sort= #{sort},
    </if>
    <if test="pwd"!=null>
        pwd= #{pwd},
    </if>
</set>
WHERE id = #{id}

1.5《TRIM》

用来：替代《where》《set》

<trim prefix = "WHERE" prefixOverrides = “AND|OR”>

<trim prefix = "SET" suffixOverrides = “,”>

1.6《FOREACH》批量删除   批量添加  批量修改

<foreach collection="list" open="(" close=")" item="id" separator=",">
</foreach>

collection:返回的一个集合

item：变量名

separator：分隔符

open：起始符

close：结束符