diff --git a/docs/script/sql/update/2026-07-20-knowledge-fragment-fid.sql b/docs/script/sql/update/2026-07-20-knowledge-fragment-fid.sql
index 58b83adb..0bb5c264 100644
--- a/docs/script/sql/update/2026-07-20-knowledge-fragment-fid.sql
+++ b/docs/script/sql/update/2026-07-20-knowledge-fragment-fid.sql
@@ -1,6 +1,14 @@
 -- RAG metadata migration (MySQL 8). Safe to execute repeatedly.
+-- 注意：MySQL 8 不支持 ALTER TABLE ... ADD COLUMN IF NOT EXISTS（仅 MariaDB 支持），
+-- 因此列的增量添加统一用 information_schema 守卫 + PREPARE 实现幂等。
+SET @add_file_hash_col = IF(EXISTS(
+    SELECT 1 FROM information_schema.columns WHERE table_schema = DATABASE()
+    AND table_name = 'knowledge_attach' AND column_name = 'file_hash'),
+    'SELECT 1',
+    'ALTER TABLE `knowledge_attach` ADD COLUMN `file_hash` varchar(64) NULL DEFAULT NULL COMMENT ''文件SHA-256摘要'' AFTER `doc_id`');
+PREPARE stmt FROM @add_file_hash_col; EXECUTE stmt; DEALLOCATE PREPARE stmt;
+
 ALTER TABLE `knowledge_attach`
-    ADD COLUMN IF NOT EXISTS `file_hash` varchar(64) NULL DEFAULT NULL COMMENT '文件SHA-256摘要' AFTER `doc_id`,
     MODIFY COLUMN `doc_id` varchar(32) NULL DEFAULT NULL COMMENT '文档ID';
 
 SET @add_file_hash = IF(EXISTS(
@@ -9,8 +17,14 @@ SET @add_file_hash = IF(EXISTS(
     'SELECT 1', 'ALTER TABLE `knowledge_attach` ADD UNIQUE INDEX `uk_knowledge_file_hash` (`knowledge_id`, `file_hash`)');
 PREPARE stmt FROM @add_file_hash; EXECUTE stmt; DEALLOCATE PREPARE stmt;
 
+SET @add_fid_col = IF(EXISTS(
+    SELECT 1 FROM information_schema.columns WHERE table_schema = DATABASE()
+    AND table_name = 'knowledge_fragment' AND column_name = 'fid'),
+    'SELECT 1',
+    'ALTER TABLE `knowledge_fragment` ADD COLUMN `fid` varchar(32) NULL DEFAULT NULL COMMENT ''向量库片段ID'' AFTER `id`');
+PREPARE stmt FROM @add_fid_col; EXECUTE stmt; DEALLOCATE PREPARE stmt;
+
 ALTER TABLE `knowledge_fragment`
-    ADD COLUMN IF NOT EXISTS `fid` varchar(32) NULL DEFAULT NULL COMMENT '向量库片段ID' AFTER `id`,
     MODIFY COLUMN `doc_id` varchar(32) NULL DEFAULT NULL COMMENT '文档ID';
 
 UPDATE `knowledge_fragment`
diff --git a/ruoyi-modules/ruoyi-chat/src/main/java/org/ruoyi/service/knowledge/impl/KnowledgeAttachServiceImpl.java b/ruoyi-modules/ruoyi-chat/src/main/java/org/ruoyi/service/knowledge/impl/KnowledgeAttachServiceImpl.java
index ed86abab..c36db0a2 100644
--- a/ruoyi-modules/ruoyi-chat/src/main/java/org/ruoyi/service/knowledge/impl/KnowledgeAttachServiceImpl.java
+++ b/ruoyi-modules/ruoyi-chat/src/main/java/org/ruoyi/service/knowledge/impl/KnowledgeAttachServiceImpl.java
@@ -215,8 +215,6 @@ public class KnowledgeAttachServiceImpl implements IKnowledgeAttachService {
                 ? DocumentSplitConfig.DEFAULT_OVERLAP : knowledgeInfoVo.getOverlapChar().intValue();
             DocumentSplitConfig splitConfig = new DocumentSplitConfig(
                 knowledgeInfoVo.getSeparator(), blockSize, overlap, attach.getType());
-            List<KnowledgeFragment> oldFragments = knowledgeFragmentMapper.selectList(
-                    Wrappers.<KnowledgeFragment>lambdaQuery().eq(KnowledgeFragment::getDocId, docId));
 
             // 获取文件信息并下载
             List<OssDTO> ossDTOs = ossService.selectByIds(String.valueOf(attach.getOssId()));
@@ -262,12 +260,11 @@ public class KnowledgeAttachServiceImpl implements IKnowledgeAttachService {
             storeEmbeddingBo.setApiKey(chatModelVo.getApiKey());
             storeEmbeddingBo.setBaseUrl(chatModelVo.getApiHost());
             try {
+                // 写入新向量前，先按 docId 清理该文档的旧向量：
+                // 历史数据的片段 fid 为迁移脚本回填的 MD5 值，与向量库中实际存储的 fid 不一致，
+                // 按 fid 删除无法命中旧向量，会导致重复向量累积；按 docId 清理对三种向量库均一致有效。
+                vectorStoreService.removeByDocId(docId, String.valueOf(knowledgeId));
                 vectorStoreService.storeEmbeddings(storeEmbeddingBo);
-                for (KnowledgeFragment old : oldFragments) {
-                    if (StringUtils.isNotBlank(old.getFid())) {
-                        vectorStoreService.removeByFid(old.getFid(), String.valueOf(knowledgeId));
-                    }
-                }
             } catch (Exception vectorError) {
                 for (String newFid : fids) {
                     try {