db2的merge into语句怎么改写成mysql的？

MERGE INTO <target> USING <source>
ON <match-condition>

WHEN MATCHED [AND <othe-condition>]
THEN [UPDATE SET ... ]

WHEN  NOT MATCHED [AND <othe-condition>]
THEN [INSERT VALUES ...]

上面db2版本的sql写成mysql是什么格式

declare
MATCHED number(10):=0;//定义MATCHED参数
begin
if MATCHED then //MATCHED是判断条件
UPDATE SET ...
else
INSERT VALUES ...
end if;
end;