-- 同一个表
UPDATE table_a SET A=(SELECT B FROM (SELECT * FROM table_a) b WHERE b.id = table_a.id)
-- 两个(一样的)表
UPDATE table_a SET A = (SELECT B FROM table_b WHERE table_b.id= table_a.id)
-- 例子
-- UPDATE FY_MEDICINE_DIRECTION SET MEDICINE_NAME=(SELECT COMMON_NAME FROM (SELECT * FROM FY_MEDICINE_DIRECTION) b WHERE b.id = FY_MEDICINE_DIRECTION.id) WHERE SOURCES='参考《国家医保药品手册》(2017版)' AND MED_ISTATUS=1
-- UPDATE message SET image=(SELECT istatus FROM (SELECT * FROM message) b WHERE b.id = message.id)