UPDATE … FROM JOIN in SQL Server

SQL Server lets you UPDATE from a JOIN. That is handy and dangerous. Write the SELECT first. When the grid is right, change SELECT to UPDATE.

Preview, then write

-- Look first
SELECT c.customer_id, c.phone, i.new_phone
FROM Customers c
JOIN ImportPhones i ON i.customer_id = c.customer_id;

-- Then, and only then
-- UPDATE c SET phone = i.new_phone
-- FROM Customers c
-- JOIN ImportPhones i ON i.customer_id = c.customer_id;