2つのテーブルにまたがるUPDATEとDELETE

1

-- Works on every engine in this list, unchanged.
UPDATE customers
SET loyalty_points = loyalty_points + 50
WHERE id IN (
  SELECT customer_id FROM orders WHERE status = 'refunded' AND total > 2000
);

2

-- The same shape when the new value comes from the other table.
UPDATE products
SET stock_quantity = stock_quantity + (
  SELECT COALESCE(SUM(change_qty), 0)
  FROM inventory_logs il
  WHERE il.product_id = products.id
    AND il.reason = 'return'
)
WHERE id IN (SELECT product_id FROM inventory_logs WHERE reason = 'return');

MySQL / MariaDB

-- The join goes between UPDATE and SET.
UPDATE customers c
  JOIN orders o ON o.customer_id = c.id
SET c.loyalty_points = c.loyalty_points + 10
WHERE o.status = 'refunded';

-- DELETE names which table's rows to remove, before FROM.
DELETE c
FROM customers c
  JOIN orders o ON o.customer_id = c.id
WHERE o.status = 'refunded';

PostgreSQL

-- The second table goes in FROM, and the join condition in WHERE.
UPDATE customers
SET loyalty_points = loyalty_points + 10
FROM orders o
WHERE o.customer_id = customers.id
  AND o.status = 'refunded';

-- DELETE uses USING rather than FROM for the extra table.
DELETE FROM wishlists
USING products p
WHERE p.id = wishlists.product_id
  AND p.stock_quantity = 0;

3

-- SQLite 3.33 (2020) and later, with PostgreSQL's spelling.
UPDATE customers
SET loyalty_points = loyalty_points + 10
FROM orders o
WHERE o.customer_id = customers.id
  AND o.status = 'refunded'
  AND o.total > 2500;

SQL Server

-- The alias is updated, and the FROM clause repeats the target table.
UPDATE c
SET c.loyalty_points = c.loyalty_points + 10
FROM customers c
  JOIN orders o ON o.customer_id = c.id
WHERE o.status = 'refunded';

DELETE c
FROM customers c
  JOIN orders o ON o.customer_id = c.id
WHERE o.status = 'refunded';

Oracle

-- Oracle has no UPDATE ... FROM and no UPDATE ... JOIN.
-- EXISTS is the portable answer, and the one to use.
UPDATE customers c
SET c.loyalty_points = c.loyalty_points + 10
WHERE EXISTS (
  SELECT 1 FROM orders o
  WHERE o.customer_id = c.id AND o.status = 'refunded'
);

DELETE FROM wishlists w
WHERE EXISTS (
  SELECT 1 FROM products p
  WHERE p.id = w.product_id AND p.stock_quantity = 0
);