/*SQL 中LEFT JOIN的含義是__,如果 tbl_user記錄了學生的姓名(name)和學號(ID)，
tbl_score記錄了學生（有的學生考試以後被開除了，沒有其記錄）的學號(ID)和考試成績(score)以及考試科目(subject)，要想打印出各個學生姓名及對應的的各科總成績，則可以用SQL語句____.
答：自然左外連線

*/
create database phpinterview;
use phpinterview
create table tbl_user
(
ID                             int                            not null,
name                           varchar(50)                    not null,
primary key (ID)
);
create table tbl_score
(
ID                             int                            not null,
score                          dec(6,2)                       not null,
subject                        varchar(20)                    not null
);
insert into tbl_user (ID, name) values (1, ‘beimu’);
insert into tbl_user (ID, name) values (2, ‘aihui’);
insert into tbl_score (ID, score, subject) values (1, 90, ‘語文’);
insert into tbl_score (ID, score, subject) values (1, 80, ‘數學’);
insert into tbl_score (ID, score, subject) values (2, 86, ‘數學’);
insert into tbl_score (ID, score, subject) values (2, 96, ‘語文’);
select A.id,sum(B.score) as sumscore
from tbl_user A left join tbl_score B
on A.ID=B.ID
group by A.id