Max 单独执行和 结合group 后的不同表现

select count(*) from item_resource_bind_his;

select nvl(max(key), 1) key from item_resource_bind_his;

select nvl(max(key), 1) key

from item_resource_bind_his t

where clear_date_time is null

group by item, so_line_num, so_num, wbs_num;

重新做个测试

-- Create table

create table TEST

(

id NUMBER,

name NVARCHAR2(111)

)

;

-- Add comments to the columns

comment on column TEST.id

is '排序';

comment on column TEST.name

is '姓名';

INSERT INTO TEST(ID, NAME)VALUES(1, '张三');

INSERT INTO TEST(ID, NAME)VALUES(2, '李四');

select * from TEST t

select max(id) id from test where id = 3