merge语句

merge语句用于进行数据合并—根据条件在表中执行数
据的修改或插入操作，如果要插入的记录在目标表中已经
存在，则执行更新操作、否则执行插入操作。
语法：
merge into table [alias]
using (table | view | sub_query) [alias]
on (join_condition)
when matched then
update set col1 = col1_val, col2 = col2_val
when not matched then
insert (column_list) values (column_values);


用法举例：
create table test1(eid number(10), name varchar2(20),birth date,salary number(8,2));
insert into test1 values (1001, '张三', '20-5月-70', 2300);
insert into test1 values (1002, '李四', '16-4月-73', 6600);
select * from test1;
create table test2(eid number(10), name varchar2(20),birth date,salary number(8,2));
select * from test2;
merge into test2
using test1
on(test1.eid = test2.eid )
when matched then
update set name = test1.name, birth = test1.birth, salary = test1.salary
when not matched then
insert (eid, name, birth, salary) values(test1.eid, test1.name, test1.birth, test1.salary);
select * from test2;