動態(tài)SQL

<select id="queryByCountryCity" resultType="com.text.pojo.Addresses">
  select * from addresses
  <where>
      <if test="country != null and country !=''">
          COUNTRY = #{country}
      </if>
      <if test="city != null and city !=''">
          and
          CITY = #{city}
      </if>
  </where>
</select>

<if>if 可以加入test=""進(jìn)行相關(guān)判斷

<where>where 可以去掉多余的前置and

<!--
    功能：
    根據(jù)傳入的對象動態(tài)的修改其中的值，
    如果某個字段傳入的非空值，再去修改，否則不修改

    set只能處理后置的
-->
<update id="update" parameterType="com.text.pojo.Addresses">
  update addresses
  <set>
      <if test="city != null and city != ''">
        city = #{city},
      </if>

      <if test="country != null and country != ''">
         country = #{country},
      </if>

      <if test="street != null and street != ''">
          street = #{street},
      </if>

      <if test="state != null and state != ''">
          state = #{state},
      </if>

      <if test="zip != null and zip != ''">
          zip = #{zip},
      </if>
  </set>
  <where>
      ADDR_ID = #{addrId}
  </where>
</update>

<set>set 除去后面的逗號,

<select id="query" resultType="com.text.pojo.Addresses" parameterType="com.text.pojo.Addresses">
  select * from addresses
  <where>
      <choose>
          <when test="country != null">
              and country = #{country}
          </when>
          <when test="state != null">
              and state = #{state}
          </when>
          <otherwise>
              and city = #{city}
          </otherwise>
      </choose>
  </where>
</select>

<choose>choose 相當(dāng)于if.. else if

<otherwise>otherwise 相當(dāng)于else

<select id="queryTrim" resultType="com.text.pojo.Addresses" parameterType="com.text.pojo.Addresses">
  select * from addresses
  <trim prefix="WHERE" suffixOverrides="AND">
      <if test="city != null and city != ''">
          city = #{city} and
      </if>

      <if test="country != null and country != ''">
          country = #{country} and
      </if>

      <if test="street != null and street != ''">
          street = #{street} and
      </if>

      <if test="state != null and state != ''">
          state = #{state} and
      </if>

      <if test="zip != null and zip != ''">
          zip = #{zip} and
      </if>
  </trim>
</select>

<trim>trim 比較全能

可以添加屬性，prefix suffix代表前面或后面加額外的sql字段

prefixOverrides suffixOverrides代表前面和后面可能有多余的sql字段

mybatis可以根據(jù)屬性自己識別

<select id="queryByIds" resultType="com.text.pojo.Addresses">
    select *
    from addresses
    <where>
        addr_id in
        <!--
            collection代表集合類型
            open代表拼接時以什么開頭
            close代表拼接時以什么結(jié)尾
            item代表遍歷的每個元素的名字，一個代號
            separator代表分隔符
            index 如果需要標(biāo)號也可以使用
        -->
        <foreach collection="list" open="(" close=")" item="item" separator=",">
          #{item}
        </foreach>
    </where>
</select>

<foreach>foreach 可以進(jìn)行遍歷

有collection open close item separator index等多種屬性

<!--#{}內(nèi)不支持拼接
    實現(xiàn)模糊查詢
    解決方案1：在應(yīng)用層進(jìn)行拼接再傳進(jìn)mapper.xml
    解決方案2：再xml中用字符串拼接 '%'+ #{city} + '%'  但是這樣有sql注入風(fēng)險
    解決方案3：通過mysql函數(shù)concat(*,*,*)實現(xiàn)拼接
    解決方案4：使用bind標(biāo)簽，對我們的變量進(jìn)行重新綁定，然后通過新綁定的變量進(jìn)行引用即可
-->
<select id="queryLike" resultType="com.text.pojo.Addresses">
    <bind name="_city" value="'%'+city+'%'"/>
    select * from addresses
    <where>
        city like #{_city}
    </where>
</select>

<bind>bind 可以進(jìn)行自定義變量

<!--將最常用的sql語句變成片段，方便復(fù)用-->
<sql id="baseColumn">
  country,state,city
</sql>

<select id="listAll" resultType="com.text.pojo.Addresses">
    select
    <include refid="baseColumn"/>
    from addresses
</select>

<sql>sql 可以取出重復(fù)的sql片段進(jìn)行復(fù)用

<include> include 可以導(dǎo)入sql片段

兩個標(biāo)簽需要配合使用