select

根據傳入的參數來決定：如果用戶名不為空，則對用戶名進行模糊查詢，如果郵箱不為空，則以郵箱為查詢條件

<select id="selectByUser" parameterType="com.tgb.mybatis.entity.SysUser" resultType="com.tgb.mybatis.entity.SysUser">selectuser_name "userName",user_password "userPassword",user_info "userInfo",head_img "headImg",create_time "createTime"fromsys_userwhere1=1<if test="userName != null and userName !=''">and user_name like CONCAT('%',#{userName},'%')</if><if test="userEmail != null and userEmail != ''">and user_email =#{userEmail}</if></select>

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update

找到id為xxx這條數據，逐個屬性判斷，如果該屬性不為空，則進行更新操作

<update id="updateById">update sys_userSET<if test="userName != null and userName !=''">user_name = #{userName},</if><if test="userPassword != null and userPassword !=''">user_password = #{userPassword},</if><if test="userEmail != null and userEmail !=''">user_email = #{userEmail},</if><if test="userInfo != null and userInfo !=''">user_info = #{userInfo},</if><if test="headImg != null and headImg !=''">head_img = #{headImg},</if><if test="createTime != null and createTime !=''">create_time =#{createTime},</if>id = #{id}whereid = #{id}</update>

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insert

<insert id="insert">insert into sys_user(user_name,user_password,<if test="userEmail !=null and userEmail != ''">user_email,</if>user_info,head_img,create_time)VALUES(#{userName},#{userPassword},<if test="userEmail != null and userEmail !=''">user_email = #{userEmail},</if>#{userInfo},#{headImg, jdbcType=BLOB},#{createTime,jdbcType=TIMESTAMP})</insert>

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關于where1=1的應用，參見我的這個博客——>一起去大廠系列】深入理解MySQL中where 1 = 1的用處

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