Update from Sync Service

数据库/去重.md

@@ -1,15 +1,57 @@
-begin tran
+# 数据去重方法
+
+> SQL Server 数据去重常用方法
+
+## 方法一：使用 DISTINCT
 
 ```sql
-select distinct * into #temp from DataSyncStationSX
-delete DataSyncStationSX
-go
-insert DataSyncStationSX select * from #temp Sqlclub
-go
-drop table #temp
-
-select * from DataSyncStationSX
+SELECT DISTINCT * FROM TableName
 ```
-order by sid
 
-commit
+## 方法二：临时表去重
+
+```sql
+BEGIN TRAN
+
+-- 1. 选中不重复的数据到临时表
+SELECT DISTINCT * INTO #temp FROM DataSyncStationSX
+
+-- 2. 删除原表数据
+DELETE FROM DataSyncStationSX
+
+-- 3. 从临时表导回
+INSERT INTO DataSyncStationSX SELECT * FROM #temp
+
+-- 4. 删除临时表
+DROP TABLE #temp
+
+COMMIT
+```
+
+## 方法三：ROW_NUMBER 去重
+
+```sql
+-- 删除重复数据，保留最新一条
+DELETE FROM TableName
+WHERE ID IN (
+    SELECT ID FROM (
+        SELECT ID, ROW_NUMBER() OVER (PARTITION BY duplicate_column ORDER BY created_time DESC) AS rn
+        FROM TableName
+    ) t
+    WHERE rn > 1
+)
+```
+
+## 方法四：查找重复数据
+
+```sql
+-- 查找重复记录
+SELECT column1, column2, COUNT(*) as cnt
+FROM TableName
+GROUP BY column1, column2
+HAVING COUNT(*) > 1
+```
+
+---
+
+> ⚠️ 执行删除前请先备份数据！