我在视图＆amp;上使用了“左连接”。子查询但在mariadb 10.2.11+中丢失了'null'行。我不知道这是怎么发生的。你能解释一下吗？
架构和数据：
create table t1 (
id int not null auto_increment,
name varchar(50),
primary key (id)
) engine = innodb auto_increment = 1 default character set = utf8;
create table t2 (
id int not null auto_increment,
pid int not null,
subname varchar(50),
primary key (id)
) engine = innodb auto_increment = 1 default character set = utf8;
insert into t1(id, name) values (1,'a'),(2,'b'),(3,'c');
insert into t2(pid, subname) values (1,'a_1'),(1,'a_2'),(1,'a_3'),
(2,'b_1'),(2,'b_2'),(2,'b_3');
create table t2_1 as
select * from t2 where id in ( select max(id) from t2 group by pid );
create view v2 as
select * from t2 where id in ( select max(id) from t2 group by pid );
在以下查询中，左表始终为t1，右表始终等于select * from t2 where id in ( select max(id) from t2 group by pid )。
使用子查询左连接：
select t1.id, t1.name, t22.id as sid, t22.subname
from t1 left join (
select * from t2 where id in ( select max(id) from t2 group by pid )
) as t22
on (t1.id = t22.pid);
结果mariadb 10.1.21没问题：
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
| 3 | c | NULL | NULL |
+----+------+------+---------+
导致mariadb 10.2.11或10.2.13错误：
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
+----+------+------+---------+
左表连接
select t1.id, t1.name, t2_1.id as sid, t2_1.subname
from t1 left join t2_1
on (t1.id = t2_1.pid);
结果mariadb 10.1.21没问题：
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
| 3 | c | NULL | NULL |
+----+------+------+---------+
结果mariadb 10.2.11或10.2.13没问题：
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
| 3 | c | NULL | NULL |
+----+------+------+---------+
左边加入视图：
select t1.id, t1.name, t22.id as sid, t22.subname
from t1 left join v2 as t22
on (t1.id = t22.pid);
结果mariadb 10.1.21没问题：
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
| 3 | c | NULL | NULL |
+----+------+------+---------+
导致mariadb 10.2.11或10.2.13错误
+----+------+------+---------+
| id | name | sid | subname |
+----+------+------+---------+
| 1 | a | 3 | a_3 |
| 2 | b | 6 | b_3 |
+----+------+------+---------+