UPDATE mlpxxb p
SET p.ssxq=(SELECT max(q.mc) FROM dd_xzqh q WHERE p.ssxqdm=q.dm)
where exists(select 1 from dd_xzqh q where p.ssxqdm=q.dm);
SET p.ssxq=(SELECT max(q.mc) FROM dd_xzqh q WHERE p.ssxqdm=q.dm)
where exists(select 1 from dd_xzqh q where p.ssxqdm=q.dm);
(
SELECT q.mc FROM dd_xzqh q WHERE p.ssxqdm = q.dm
)
(SELECT q.mc FROM dd_xzqh q WHERE mlpxxb.ssxqdm = q.dm)