How to Update Rows in PostgreSQL

RETURNING makes UPDATE report back the rows it changed, so you can confirm the effect in the same round trip instead of following up with a SELECT. It accepts any expression and pairs well with a transaction you can roll back if the output looks wrong.

UPDATE orders
SET status = 'shipped'
WHERE id = 42
RETURNING id, status;

Update from another table

The FROM clause joins another table into the update. The critical detail is that the join condition lives in WHERE, and leaving it out cross-joins the tables so every row gets a value from an arbitrary match. If one order matches several customers, Postgres picks one non-deterministically rather than raising an error.

UPDATE orders o
SET region = c.region
FROM customers c
WHERE c.id = o.customer_id;