diff --git a/backend/src/utils/tenantFullExport.ts b/backend/src/utils/tenantFullExport.ts
index e8ab4be..523099b 100644
--- a/backend/src/utils/tenantFullExport.ts
+++ b/backend/src/utils/tenantFullExport.ts
@@ -1025,41 +1025,14 @@ export const importTenantFullExportArchive = async (
     archiveBuffer: Buffer,
     options: ImportOptions = {}
 ): Promise<ImportResult> => {
+    const rawExportData = await readTenantFullExportArchive(archiveBuffer)
+    const exportData = remapTenantScopedExport(rawExportData, options.targetTenantId)
     const reader = new ZipReader(new BlobReader(new Blob([archiveBuffer])))
 
     try {
         const entries = await reader.getEntries()
         const entriesByName = new Map(entries.map((entry: any) => [entry.filename, entry]))
         const manifest = JSON.parse(await readZipTextEntry(entriesByName, "manifest.json")) as TenantArchiveManifest
-
-        if (manifest?.format !== "fedeo.tenant-archive-export" || manifest.version !== 1) {
-            throw new Error("Ungültiges FEDEO Mandantenarchiv-Format")
-        }
-
-        const tables: TableRows = {}
-        for (const table of manifest.tables || []) {
-            tables[table.name] = JSON.parse(await readZipTextEntry(entriesByName, table.path))
-        }
-
-        const rawExportData: TenantFullExport = {
-            format: "fedeo.tenant-full-export",
-            version: 1,
-            exportedAt: manifest.exportedAt,
-            tenantId: manifest.tenantId,
-            tables,
-            files: (manifest.files || []).map((file) => ({
-                id: file.id,
-                path: file.path,
-                name: file.name,
-                mimeType: file.mimeType,
-                size: file.size,
-                contentBase64: null,
-                missing: file.missing,
-                error: file.error,
-            })),
-        }
-
-        const exportData = remapTenantScopedExport(rawExportData, options.targetTenantId)
         const sourceTenantId = rawExportData.tenantId
         const targetTenantId = exportData.tenantId
         const sourcePrefix = `${sourceTenantId}/`
@@ -1086,3 +1059,43 @@ export const importTenantFullExportArchive = async (
         await reader.close()
     }
 }
+
+export const readTenantFullExportArchive = async (archiveBuffer: Buffer): Promise<TenantFullExport> => {
+    const reader = new ZipReader(new BlobReader(new Blob([archiveBuffer])))
+
+    try {
+        const entries = await reader.getEntries()
+        const entriesByName = new Map(entries.map((entry: any) => [entry.filename, entry]))
+        const manifest = JSON.parse(await readZipTextEntry(entriesByName, "manifest.json")) as TenantArchiveManifest
+
+        if (manifest?.format !== "fedeo.tenant-archive-export" || manifest.version !== 1) {
+            throw new Error("Ungültiges FEDEO Mandantenarchiv-Format")
+        }
+
+        const tables: TableRows = {}
+        for (const table of manifest.tables || []) {
+            tables[table.name] = JSON.parse(await readZipTextEntry(entriesByName, table.path))
+        }
+
+        return {
+            format: "fedeo.tenant-full-export",
+            version: 1,
+            exportedAt: manifest.exportedAt,
+            tenantId: manifest.tenantId,
+            tables,
+            files: (manifest.files || []).map((file) => ({
+                id: file.id,
+                path: file.path,
+                name: file.name,
+                mimeType: file.mimeType,
+                size: file.size,
+                contentBase64: null,
+                missing: file.missing,
+                error: file.error,
+            })),
+        }
+
+    } finally {
+        await reader.close()
+    }
+}
diff --git a/backend/src/utils/tenantMergeService.ts b/backend/src/utils/tenantMergeService.ts
new file mode 100644
index 0000000..0c99102
--- /dev/null
+++ b/backend/src/utils/tenantMergeService.ts
@@ -0,0 +1,124 @@
+import { pool } from "../../db"
+import type { TenantFullExport } from "./tenantFullExport"
+import { buildTenantMergePlan, type TenantMergePlan, type TenantMergeTableMetadata } from "./tenantMergePlan"
+
+type MergeDatabaseMetadata = TenantMergeTableMetadata & {
+    columns: string[]
+}
+
+const quoteIdent = (value: string) => `"${value.replace(/"/g, '""')}"`
+const globalNaturalKeyTables = new Set(["accounts", "units", "countrys", "citys"])
+
+const loadMergeMetadata = async (client: any) => {
+    const columnsResult = await client.query(`
+        select table_name, column_name
+        from information_schema.columns
+        where table_schema = 'public'
+        order by table_name, ordinal_position
+    `)
+    const primaryKeyResult = await client.query(`
+        select tc.table_name, kcu.column_name
+        from information_schema.table_constraints tc
+        join information_schema.key_column_usage kcu
+          on tc.constraint_name = kcu.constraint_name
+         and tc.constraint_schema = kcu.constraint_schema
+        where tc.table_schema = 'public' and tc.constraint_type = 'PRIMARY KEY'
+        order by tc.table_name, kcu.ordinal_position
+    `)
+    const metadata: Record<string, MergeDatabaseMetadata> = {}
+
+    for (const row of columnsResult.rows) {
+        metadata[row.table_name] ||= { columns: [], primaryKey: [] }
+        metadata[row.table_name].columns.push(row.column_name)
+    }
+    for (const row of primaryKeyResult.rows) {
+        metadata[row.table_name] ||= { columns: [], primaryKey: [] }
+        metadata[row.table_name].primaryKey.push(row.column_name)
+    }
+
+    return metadata
+}
+
+const remapSourceTenant = (exportData: TenantFullExport, targetTenantId: number) => {
+    const tables: Record<string, Record<string, any>[]> = {}
+
+    for (const [table, rows] of Object.entries(exportData.tables || {})) {
+        tables[table] = rows.map((row) => {
+            const next = { ...row }
+            if (table === "tenants" && Number(next.id) === Number(exportData.tenantId)) next.id = targetTenantId
+            if (Number(next.tenant) === Number(exportData.tenantId)) next.tenant = targetTenantId
+            if (Number(next.tenant_id) === Number(exportData.tenantId)) next.tenant_id = targetTenantId
+            return next
+        })
+    }
+
+    return tables
+}
+
+const loadTargetRows = async (
+    client: any,
+    table: string,
+    sourceRows: Record<string, any>[],
+    metadata: MergeDatabaseMetadata,
+    targetTenantId: number
+) => {
+    if (!sourceRows.length) return []
+    if (table === "tenants") {
+        return (await client.query(`select * from ${quoteIdent(table)} where ${quoteIdent("id")} = $1`, [targetTenantId])).rows
+    }
+
+    const tenantColumn = metadata.columns.includes("tenant")
+        ? "tenant"
+        : metadata.columns.includes("tenant_id") ? "tenant_id" : null
+    if (tenantColumn) {
+        return (await client.query(
+            `select * from ${quoteIdent(table)} where ${quoteIdent(tenantColumn)} = $1`,
+            [targetTenantId]
+        )).rows
+    }
+    if (globalNaturalKeyTables.has(table)) {
+        return (await client.query(`select * from ${quoteIdent(table)}`)).rows
+    }
+
+    if (metadata.primaryKey.length === 1) {
+        const key = metadata.primaryKey[0]
+        const values = Array.from(new Set(sourceRows.map((row) => row[key]).filter((value) => value !== null && typeof value !== "undefined").map(String)))
+        if (!values.length) return []
+        return (await client.query(
+            `select * from ${quoteIdent(table)} where ${quoteIdent(key)}::text = any($1::text[])`,
+            [values]
+        )).rows
+    }
+
+    return (await client.query(`select * from ${quoteIdent(table)}`)).rows
+}
+
+export const createTenantMergeDryRunWithClient = async (
+    client: any,
+    exportData: TenantFullExport,
+    targetTenantId: number
+): Promise<TenantMergePlan> => {
+    const metadata = await loadMergeMetadata(client)
+    const sourceTables = remapSourceTenant(exportData, targetTenantId)
+    const targetTables: Record<string, Record<string, any>[]> = {}
+
+    for (const [table, sourceRows] of Object.entries(sourceTables)) {
+        const tableMetadata = metadata[table]
+        if (!tableMetadata) continue
+        targetTables[table] = await loadTargetRows(client, table, sourceRows, tableMetadata, targetTenantId)
+    }
+
+    return buildTenantMergePlan(sourceTables, targetTables, metadata)
+}
+
+export const createTenantMergeDryRun = async (
+    exportData: TenantFullExport,
+    targetTenantId: number
+) => {
+    const client = await pool.connect()
+    try {
+        return await createTenantMergeDryRunWithClient(client, exportData, targetTenantId)
+    } finally {
+        client.release()
+    }
+}