# SQL Server: Update Only When Values Change

> Avoid unnecessary writes and locking by updating rows only when values differ.

- URL: https://webdevrock.uk/snippets/sql-update-only-when-changed/
- Tags: sql, sql-server, performance, data-fix
- Updated: 2026-02-16
- Requires: SQL Server 2008+

## Problem

A bulk update runs successfully but updates every matching row, even when the value has not changed. This increases locking, transaction log usage, and can trigger unnecessary downstream processes.

## Solution

Add a comparison condition so only genuinely changed rows are updated.

```sql
UPDATE t
SET t.some_column = tu.new_some_column
FROM target_table t
JOIN #temp_updates tu ON tu.id = t.id
WHERE
    t.some_column <> tu.new_some_column
    OR t.some_column IS NULL;
```

[Generate this change-only update with a backup and rollback in the Data Fix Script Builder](https://webdevrock.uk/tools/data-fix-script/)

## Notes

- Reduces transaction log growth during large updates.
- Minimises locking and index churn.
- Particularly useful when updates trigger audit logs or change tracking.
- Always preview with a SELECT first:

```sql
SELECT *
FROM target_table t
JOIN #temp_updates tu ON tu.id = t.id
WHERE
    t.some_column <> tu.new_some_column
    OR t.some_column IS NULL;

```