Merge into用法
简单的例子：好记性不如烂笔头
其基本语法规则是
merge into 目标表 a
using 源表 b
on(a.条件字段1=b.条件字段1 and a.条件字段2=b.条件字段2 ……)
when matched then update set a.更新字段=b.字段
when not macthed then insert into a(字段1,字段2……)values(值1,值2……)
MERGE INTO table T1
USING (SELECT '90040124' AS a FROM dual) T2
ON ( T1.COM_CODE=T2.a)
WHEN MATCHED THEN
UPDATE SET T1.UPDATETIME = sysdate
WHEN NOT MATCHED THEN