refactor(mapper):优化查询逻辑并处理空列表情况

- 将 filterExistingRelations 查询中的 if 判断替换为 choose-when 结构
- 在 otherwise 分支中添加空结果集查询，避免空列表时 SQL 异常- 统一 filterValidSourceRelations 查询结构，增强代码一致性
-修正 foreach 标签中 UNION ALL 前后的空格问题，确保 SQL 语法正确- 提升 XML 映射文件的可读性和健壮性

src/main/resources/mapper/SourceMapper.xml

@@ -17,7 +17,8 @@
         </foreach>
     </insert>
     <select id="filterExistingRelations" resultType="com.ycwl.basic.model.pc.source.entity.MemberSourceEntity">
-        <if test="list != null and list.size() > 0">
+        <choose>
+            <when test="list != null and list.size() > 0">
                 SELECT 
                     r.memberId as memberId, 
                     r.sourceId as sourceId, 
@@ -49,13 +50,28 @@
                       AND ms.type = r.type 
                       AND ms.face_id = r.faceId
                 )
-        </if>
+            </when>
+            <otherwise>
+                SELECT 
+                    NULL as memberId, 
+                    NULL as sourceId, 
+                    NULL as type, 
+                    NULL as faceId, 
+                    NULL as scenicId,
+                    NULL as isBuy, 
+                    NULL as orderId, 
+                    NULL as isFree,
+                    NULL as id
+                WHERE 1 = 0
+            </otherwise>
+        </choose>
     </select>
     <select id="sourceExists" resultType="boolean">
         SELECT COUNT(1) > 0 FROM source WHERE id = #{sourceId}
     </select>
     <select id="filterValidSourceRelations" resultType="com.ycwl.basic.model.pc.source.entity.MemberSourceEntity">
-        <if test="list != null and list.size() > 0">
+        <choose>
+            <when test="list != null and list.size() > 0">
                 SELECT 
                     r.memberId as memberId, 
                     r.sourceId as sourceId, 
@@ -83,7 +99,21 @@
                 WHERE EXISTS (
                     SELECT 1 FROM source s WHERE s.id = r.sourceId
                 )
-        </if>
+            </when>
+            <otherwise>
+                SELECT 
+                    NULL as memberId, 
+                    NULL as sourceId, 
+                    NULL as type, 
+                    NULL as faceId, 
+                    NULL as scenicId,
+                    NULL as isBuy, 
+                    NULL as orderId, 
+                    NULL as isFree,
+                    NULL as id
+                WHERE 1 = 0
+            </otherwise>
+        </choose>
     </select>
     <insert id="addSourceWatermark">
         insert source_watermark(source_id, face_id, watermark_type, watermark_url)