--a, b具有相同的code, 将a.name值, 全部更新为 b.NAME值
UPDATE a SET a.NAME =
(SELECT b.NAME FROM b WHERE b.code = a.code)
WHERE EXISTS (SELECT 1 FROM b WHERE b.code = a.code)



执行结果:

--a, b具有相同的code, 将a.name值, 全部更新为 b.NAME值
UPDATE a SET a.NAME =
(SELECT b.NAME FROM b WHERE b.code = a.code)
WHERE EXISTS (SELECT 1 FROM b WHERE b.code = a.code)
执行结果: