标签：error for 前台 info order 财务部 class uname arc
目录
group by分组指的是：将所有表记录按照某个相同字段进行归类
用法：
select 聚合函数,选取的字段 from 表名 group by 选择分组的字段 having 条件
聚合函数：count/sum/max/min/avg
having：表示对group by之后的数据，进行再一次的筛选
注意：group by必须和集合函数一起使用。
where 条件语句和groupby分组语句的先后顺序：
where > group by > having(*********)
实例：
mysql> select depart_id,avg(age) from employee group by depart_id ;
+-----------+----------+
| depart_id | avg(age) |
+-----------+----------+
| 1 | 45.2500 |
| 2 | 30.0000 |
| 3 | 20.0000 |
+-----------+----------+
3 rows in set (0.00 sec)
mysql> select depart_id,avg(age) from employee group by depart_id having avg(age) > 35;
+-----------+----------+
| depart_id | avg(age) |
+-----------+----------+
| 1 | 45.2500 |
+-----------+----------+
1 row in set (0.00 sec)order byorder by对查询的结果进行排序
用法：
order by 字段名 asc/desc ，其中asc默认的表示升序排序，desc表示降序排序order by age desc , id asc，则先对age进行降序排序，如果排完序记录中有相同的age时，再把有相同的这些行按id升序排序。limitlimit 参数1 , 参数2 。参数1表示行索引，从该行开始，表记录第第一行数据的索引是0，往下递增，参数2表示取多少行。以上高级用法的使用顺序是：
select * from 表名 where 条件 group by 条件 having 条件 order by 条件 limit 条件;
where > group by > having > order by > limit
使用外键的原因：
使用方法：
constraint 外键名 foreign key (被约束的字段) references 约束的表(约束的字段)
实例：
create table department(
id int auto_increment primary key,
name varchar(32) not null default ''
)charset utf8;
insert into department (name) values ('研发部');
insert into department (name) values ('运维部');
insert into department (name) values ('前台部');
insert into department (name) values ('小卖部');
create table userinfo (
id int auto_increment primary key,
name varchar(32) not null default '',
depart_id int not null default 1,
constraint fk_user_depart foreign key (depart_id) references department(id),
)charset utf8;
insert into userinfo (name, depart_id) values ('zekai', 1);
insert into userinfo (name, depart_id) values ('xxx', 2);
insert into userinfo (name, depart_id) values ('zekai1', 3);
insert into userinfo (name, depart_id) values ('zekai2', 4);
insert into userinfo (name, depart_id) values ('zekai3', 1);
insert into userinfo (name, depart_id) values ('zekai4', 2);
insert into userinfo (name, depart_id) values ('zekai4', 5);实例：
create table boy (
id int auto_increment primary key,
bname varchar(32) not null default ''
)charset utf8;
insert into boy (bname) values ('zhangsan'),('lisi'),('zhaoliu');
create table girl (
id int auto_increment primary key,
gname varchar(32) not null default ''
)charset utf8;
insert into girl (gname) values ('cuihua'),('gangdan'),('jianguo');
create table boy2girl (
id int auto_increment primary key,
bid int not null default 1,
gid int not null default 1,
constraint fk_boy2girl_boy foreign key (bid) references boy(id),
constraint fk_boy2girl_girl foreign key (gid) references girl(id)
)charset utf8;
insert into boy2girl (bid, gid) values (1,1),(1,2),(2,3),(3,3),(2,2);
select * from boy left join boy2girl on boy.id = boy2girl.bid left join girl on girl.id=boy2girl.gid;
mysql> select * from boy left join boy2girl on boy.id = boy2girl.bid left join girl on girl.id=boy2girl.gid;
+----+----------+------+------+------+------+---------+
| id | bname | id | bid | gid | id | gname |
+----+----------+------+------+------+------+---------+
| 1 | zhangsan | 1 | 1 | 1 | 1 | cuihua |
| 1 | zhangsan | 2 | 1 | 2 | 2 | gangdan |
| 2 | lisi | 5 | 2 | 2 | 2 | gangdan |
| 2 | lisi | 3 | 2 | 3 | 3 | jianguo |
| 3 | zhaoliu | 4 | 3 | 3 | 3 | jianguo |
+----+----------+------+------+------+------+---------+
5 rows in set (0.00 sec)
mysql> select bname, gname from boy left join boy2girl on boy.id = boy2girl.bid left join girl on girl.id=boy2girl.gid;
+----------+---------+
| bname | gname |
+----------+---------+
| zhangsan | cuihua |
| zhangsan | gangdan |
| lisi | gangdan |
| lisi | jianguo |
| zhaoliu | jianguo |
+----------+---------+
5 rows in set (0.00 sec)
mysql> select bname, gname from boy left join boy2girl on boy.id = boy2girl.bid left join girl on girl.id=boy2girl.gid where bname='zhangsan';
+----------+---------+
| bname | gname |
+----------+---------+
| zhangsan | cuihua |
| zhangsan | gangdan |
+----------+---------+
2 rows in set (0.02 sec)实例：
user :
id name age
1 zekai 18
2 zhangsan 23
3 xxxx 19
由于salary是比较敏感的字段，因此我们需要将此字段单独拆出来， 变成一张独立的表
private：
id salary uid (外键 + unique)
1 5000 1
2 6000 2
3 3000 3
create table user (
id int auto_increment primary key,
name varchar(32) not null default ''
)charset=utf8;
insert into user (name) values ('zhangsan'),('zekai'),('kkk');
create table priv(
id int auto_increment primary key,
salary int not null default 0,
uid int not null default 1,
constraint fk_priv_user foreign key (uid) references user(id),
unique(uid)
)charset=utf8;
insert into priv (salary, uid) values (2000, 1);
insert into priv (salary, uid) values (2800, 2);
insert into priv (salary, uid) values (3000, 3);
insert into priv (salary, uid) values (6000, 1);
ERROR 1062 (23000): Duplicate entry '1' for key 'uid'left join...on表示已left左边的表为主，会把左边的表中的信息全部显示，被join的表按照左边的表的数据一一对应显示。
实例
# 原表
mysql> select * from department;
+----+--------+
| id | name |
+----+--------+
| 1 | 研发部 |
| 2 | 运维部 |
| 3 | 前台部 |
| 4 | 小卖部 |
+----+--------+
4 rows in set (0.07 sec)
mysql> select * from userinfo;
+----+--------+-----------+
| id | name | depart_id |
+----+--------+-----------+
| 1 | zekai | 1 |
| 2 | xxx | 2 |
| 3 | zekai1 | 3 |
| 4 | zekai2 | 4 |
| 5 | zekai3 | 1 |
| 6 | zekai4 | 2 |
+----+--------+-----------+
6 rows in set (0.00 sec)
# 联表查询：
# 错误写法
mysql> select name from userinfo left join department on depart_id = department.id;
ERROR 1052 (23000): Column 'name' in field list is ambiguous
# 正确写法
mysql> select userinfo.name as uname, department.name as dname from userinfo left join department on depart_id = department.id;
# 查询结果
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
+--------+--------+
6 rows in set (0.00 sec)right join...on表示已right右边的表为主，会把右边的表中的信息全部显示，被join的表按照右边的表的数据一一对应显示。
实例：
mysql> insert into department (name) values ('财务部');
Query OK, 1 row affected (0.04 sec)
mysql>
mysql> select * from department; );
+----+--------+
| id | name |
+----+--------+
| 1 | 研发部 |
| 2 | 运维部 |
| 3 | 前台部 |
| 4 | 小卖部 |
| 5 | 财务部 |
+----+--------+
5 rows in set (0.00 sec)
mysql> select * from userinfo;
+----+--------+-----------+
| id | name | depart_id |
+----+--------+-----------+
| 1 | zekai | 1 |
| 2 | xxx | 2 |
| 3 | zekai1 | 3 |
| 4 | zekai2 | 4 |
| 5 | zekai3 | 1 |
| 6 | zekai4 | 2 |
+----+--------+-----------+
6 rows in set (0.00 sec)
mysql> select userinfo.name as uname, department.name as dname from userinfo left join department on depart_id = department.id;
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
+--------+--------+
6 rows in set (0.00 sec)
mysql> select userinfo.name as uname, department.name as dname from userinfo right join department on depart_id = department.id;
+--------+--------+
| uname | dname |
+--------+--------+
| zekai | 研发部 |
| zekai3 | 研发部 |
| xxx | 运维部 |
| zekai4 | 运维部 |
| zekai1 | 前台部 |
| zekai2 | 小卖部 |
| NULL | 财务部 |
+--------+--------+
7 rows in set (0.00 sec)inner join...on实例：
mysql> select * from department inner join userinfo on department.id=userinfo.depart_id;
+----+--------+----+--------+-----------+
| id | name | id | name | depart_id |
+----+--------+----+--------+-----------+
| 1 | 研发部 | 1 | zekai | 1 |
| 1 | 研发部 | 5 | zekai3 | 1 |
| 2 | 运维部 | 2 | xxx | 2 |
| 2 | 运维部 | 6 | zekai4 | 2 |
| 3 | 前台部 | 3 | zekai1 | 3 |
| 4 | 小卖部 | 4 | zekai2 | 4 |
+----+--------+----+--------+-----------+
6 rows in set (0.00 sec)标签：error for 前台 info order 财务部 class uname arc
原文地址：https://www.cnblogs.com/Mcoming/p/11766291.html
