mybatis里 mapping.xml l里写sql语句

if 的用法

 <select id="dynamicIfTest" parameterType="Blog" resultType="Blog">
        select * from t_blog where 1 = 1
        <if test="title != null">
            and title = #{title}
        </if>
        <if test="content != null">
            and content = #{content}
        </if>
        <if test="owner != null">
            and owner = #{owner}
        </if>
    </select>

2.3 if 和 set 使用组合更新 update

 <update id="updateZSInfo" parameterType="map">
        UPDATE tb_OrdinaryUser 
          <set>
             <if test="UserName != null">
               UserName = #{UserName},
             </if>
             <if test="Phone != null">
               Phone = #{Phone},
             </if>
             <if test="Email != null">
               Email = #{Email},
             </if>
           </set> 
        WHERE userID = #{UserId} 
    </update>

三 . trim 关键字的使用
3.1 trim 替代 where

 <select id="if_trim" resultMap="studentEntity">  
    SELECT ST.STUDENT_ID,  
           ST.STUDENT_NAME,  
         FROM STUDENT_TBL ST   
       <trim prefix="WHERE" prefixOverrides="AND|OR">  
        <if test="studentName !=null ">  
            ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')  
        </if>  
        <if test="studentSex != null and studentSex != '' ">  
            AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}  
        </if>  
        <if test="studentBirthday != null ">  
            AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}  
        </if>  
       </trim>     
    </select>

3.2 trim代替 set

 <update id="update_trim" parameterType="StudentEntity">  
    UPDATE STUDENT_TBL  
        <trim prefix="SET" suffixOverrides=",">  
            <if test="studentName != null and studentName != '' ">  
                STUDENT_TBL.STUDENT_NAME = #{studentName},  
            </if>  
            <if test="studentSex != null and studentSex != '' ">  
                STUDENT_TBL.STUDENT_SEX = #{studentSex},  
            </if>  
        </trim>  
    WHERE STUDENT_TBL.STUDENT_ID = #{studentId}  
  </update>

四 . choose
4.1 choose 是集合 when 和 otherwise 使用的

<select id="choose" resultMap="studentEntity" parameterType="StudentEntity">  
    SELECT ST.STUDENT_ID,  
           ST.STUDENT_NAME,  
      FROM STUDENT_TBL ST   
    <where>  
        <choose>  
            <when test="studentName !=null ">  
                ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')  
            </when >  
            <when test="studentBirthday != null ">  
                AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}  
            </when >  
            <otherwise>  


            </otherwise>  
        </choose>  
    </where>    
</select>

链接 https://blog.csdn.net/kongbaidepao/article/details/48056449

mybatis里 mapping.xml l里写sql语句

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