mysql基础之mariadb对表中数据的增删改查
阅读原文时间:2022年04月22日阅读:1

复习:

查看表:show tables;   创建表:create table 表名(字符类型);   删除表:drop table 表名;

对表的结构进行增删改查:

查看表结构:desc 表名;  修改表-添加字段:alter table 表名;  

修改表-修改字段:不重命名版:alter table 表名 modify 列名 类型及约束;

修改表-修改字段:重命名版:alter table 表名 change 原名 新名 类型及约束;

修改表-删除字段:alter table 表名 drop 列名;

一、增加表中的数据(insert)

insert语句的语法:insert into tablename(字段1名称,字段2名称,…) values(字段1值,字段2值,…)

1、全列插入

--insert into 表名 values(..)
--主键字段 可以用0 null default 来站位
例子:向test表中插入一条信息(数据与字段要一一对应)
MariaDB [ren]> insert into test values ('谢霆锋',188,38,1);
Query OK, 1 row affected (0.01 sec)

MariaDB [ren]> select * from test;
+-----------+------+------+------+
| name | high | age | id |
+-----------+------+------+------+
| 任彦忠 | NULL | 0 | NULL |
| 哈哈 | NULL | 66 | NULL |
| 胡歌 | NULL | 38 | NULL |
| 谢霆锋 | 188 | 38 | 1 |
+-----------+------+------+------+
4 rows in set (0.00 sec)

2、部分插入(主键不能为空)

MariaDB [ren]> insert into test (name,age) values ('张一山',26);
Query OK, 1 row affected (0.00 sec)
MariaDB [ren]> select * from test;
+-----------+------+------+------+
| name | high | age | id |
+-----------+------+------+------+
| 任彦忠 | NULL | 0 | NULL |
| 哈哈 | NULL | 66 | NULL |
| 张一山 | NULL | 26 | NULL |
| 胡歌 | NULL | 38 | NULL |
| 谢霆锋 | 188 | 38 | 1 |
+-----------+------+------+------+
5 rows in set (0.00 sec)

3、部分插入多条记录

MariaDB [ren]> insert into test (name,age) values ('杨紫',20),('老毕',11);

4、另一种插入数据的语法

insert into tablename set 字段1名称=字段1值,字段2名称=字段值

MariaDB [ren]> insert into test set name='小磐',age=20,id=2;

使用set的方式插入数据时,insert语句中字段的顺序可以与表中的字段顺序不同,而第一种语法中,字段顺序必须与表中的字段顺序相同。

5、aql_mode的模式:

ANSI:宽松模式,对插入数据进行校验,如果不符合定义类型 或长度,对数值截断保存,报警告信息,默认模式;

STRICT_TRANS_TABLES:只在事务型表中进行严格限制;

STRICT_ALL_TABLES:对所有表进行严格限制;

TRADITIONAL:严格模式,当插入数据时,进行数据的严格校验,错误的数据将不能被插入,报error错误。用于事务时,会进行事务的回滚,官方提醒我们说,如果我们使用的存储引擎是非事务型的存储引擎(比如myisam),当我们使用这种模式时,如果执行非法的插入或更新数据操作时,可能会出现部分完成的情况。

二、删除表中的数据(delete)

删除数据需要通过where子句给定删除的范围

1、物理删除

delete from 表名 where 条件

MariaDB [ren]> delete from test where name='哈哈';

2、模糊删除(不建议使用)

MariaDB [ren]> delete from test where name rlike '.*彦*';

like:like的内容不是正则,而是通配符。eg:like "%12__";A like '%abc%' or A like '%cba%'

rlike:rlike的内容可以是正则。(需要转义)eg:rlike ".*12.*" ;A rlike '.*(abc|cba).*'

3、从test表中找出age>30的数据行,然后将这些行按照age进行降序排列,排列后删除第一个

delete from test where age > 30 order by age desc limit 1;

4、清空表数据

truncate [table] 表名; #无法恢复数据,并且清空自增
delete from 表名; #在一定条件下可以恢复数据,不会清除自增

5、逻辑删除

用一条字段来表示这条信息是否已经不能再使用了

-- 给test表添加一个is_delete字段 bit 类型
alter table test add is_delete bit default 0;

三、修改表中的数据(update)

修改数据也需要通过where子句给定修改的范围

update 表名 set 列1=值1, 列2=值2… where 条件;

1、如果不加where,则是修改的表中所有记录的该字段的数据

MariaDB [ren]> update test set age=30;
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3 Changed: 3 Warnings: 0

MariaDB [ren]> select * from test;
+-----------+------+------+------+
| name | high | age | id |
+-----------+------+------+------+
| 张柏芝 | 177 | 30 | 3 |
| 王菲 | 177 | 30 | 2 |
| 谢霆锋 | 188 | 30 | 1 |
+-----------+------+------+------+
3 rows in set (0.00 sec)

2、修改一个字段的值

MariaDB [ren]> update test set high=180 where id=3;

3、修改多个字段的值

MariaDB [ren]> update test set high=180,name='李晓丽' where id=3;

四、查询数据(select)(条件,排序,聚合函数,分组,分页)

创建表并写入数据:

--创建学生表
create table students (
id int unsigned not null auto_increment primary key,
name varchar(20) default '',
age tinyint unsigned default 0,
high decimal(5,2),
gender enum('男', '女', '中性', '保密') default '保密',
cls_id int unsigned default 0,
is_delete bit default 0
);

--创建班级表
create table classes(
id int unsigned auto_increment primary key not null,
name varchar(20) not null
);

--往students表里插入数据
insert into students values
(0,'小明',18,180.00,1,1,0),
(0,'小月月',19,180.00,1,2,0),
(0,'彭于晏',28,185.00,1,1,0),
(0,'刘德华',58,175.00,1,2,0),
(0,'黄蓉',108,160.00,2,1,0),
(0,'凤姐',44,150.00,4,2,1),
(0,'王祖贤',52,170.00,2,1,1),
(0,'周杰伦儿',34,null,1,1,0),
(0,'程坤',44,181.00,1,2,0),
(0,'和珅',55,166.00,1,2,0),
(0,'刘亦菲',29,162.00,2,3,0),
(0,'金星',45,180.00,3,4,0),
(0,'静香',18,170.00,2,4,0),
(0,'郭靖',22,167.00,1,5,0),
(0,'周杰',33,178.00,1,1,0),
(0,'钱小豪',56,178.00,1,1,0),
(0,'谢霆锋',38,175.00,1,1,0),
(0,'陈冠希',38,175.00,1,1,0);

--向classes表里插入数据
insert into classes values (0, '云唯_01期'),(0, '云唯_02期');

(一)简单查询

1、查询所有列

--select * from 表名;
select * from students;

2、查询制定列

select id,name from students;

3、使用as给字段起别名

select id,name as '姓名', age, high, gender from students;

4、通过表名字段查询

select students.name from students;

5、给表起别名

select s.id,s.name,s.age from students as s;

6、消除重复行

-- distinct(/dɪ'stɪŋkt/)有区别的,独特的,明显的
select distinct age from students;

(二)条件查询

1、一定条件查询

select * from where id=5;

select * from where age !=38;

2、比较运算符

-- 查询年纪大于18岁的信息
select * from students where age > 18;

--18岁到28岁之间(and)
select * from students where age >= 18 and age =< 28;
select * from students where age between 18 and 28

--不在18岁到28岁之间(and)
select * from students where age < 18 or age > 28;
select * from students where age not between 18 and 28;

--在18岁以上或者身高180以上的人(or)
select * from students where age > 18 or high > 180;

(三)模糊查询

-- like(rlike)
-- % 替代1个或者多个甚至是没有
--_表示一个字符
-- 查询姓名中有‘小’的所有名字
select * from students where name like '%小%';
-- 查询两个字人的名字
select * from students where name like '__';
-- 查询至少有2个字的名字
select * from students where name like '%__%';
--查询name字段以t开头的所有数据
select * from students where name rlike '^t.*';

(四)范围查询

-- in (1,3,8)表示在一个非连续的范围内
-- 查询 年纪为18和34的人
select * from students where age in (18, 34);
--查询 年龄在17岁到34岁之间的信息
select * from students where age between 17 and 34;
--查询 年纪不在18到34岁的信息
select * from students where age not between 17 and 34;

(五)空判断

-- 判断is null
-- 查询身高为空的信息
select * from students where high is null;
-- 判断非空is not null
select * from students where high is not null;

(六)排序

-- order by 字段
-- asc从小到大排列,即升序(ascend,上升,升入,追溯)
-- desc从大到小排序,即降序(descend,下降,下去,下来)
-- 查询年纪在18到34岁之间的男性,按照年纪从小到大
select * from students where gender=1 and age between 18 and 34 order by age;
-- 查询年纪在18到34岁之间的女性,身高从高到矮
select * from students where gender=2 and age between 18 and 34 order by high desc;
-- order by 多字段
-- 查询年纪在18到34岁的女性,身高从高到矮排序,如果身高相同的情况下按照年纪从小到大排序
select * from students where age between 18 and 34 and gender=2 order by high desc;
-- 查询年纪在18到34岁的男性,身高从高到矮排序,如果身高相同的情况下按照年纪从小到大排序,如果年龄也相等那么按照id从小到大排序;
select * from students where age between 18 and 34 and gender=1 order by high desc, age, id asc;

(七)聚合函数

-- 总数
-- count
-- 查询男性有多少人
select count(*) from students where gender=1;
-- 最大值
-- max
-- 查询最大的年纪
select max(age) from students;
-- 查询女性的最高 身高
select max(high) from students where gender=2;
-- 最小值
-- min
select min(high) from students;
-- 求和
-- sum
-- 计算所有人的年龄总和
select sum(age) from students;
-- 平均值
-- avg(average)
-- 计算平均年纪
-- 计算平均年纪 sum(age)/count(*)
select sum(age)/count(*) from students;
select avg(age) from students;
-- 保留2位小数round(圆的,整数的)
select round(avg(age),2) from students;

(八)分组

-- group by
-- 按照性别分组,查询所有的性别
select gender from students group by gender;
-- 计算每组性别的人数
select gender, count(*) from students group by gender;
-- 查询男性组中的姓名 group_concat(合并多个数组;合并多个字符串)
select gender,group_concat(name) from students where gender=1 group by gender;
-- having
-- 查询每个性别平均年纪超过30岁的性别,以及姓名 having avg(age) > 30
select gender, group_concat(name) from students group by gender having avg(age) > 30;
-- 查询每种性别中的人数多于4个的组的信息
select gender,group_concat(name) from students group by gender having count(*)>4;

(九)分页

-- limit:限制,限定
-- 显示5页
select * from students limit 5;
-- 分页显示,每页显示2条数据(0表示从第一行开始显示,2表示显示两行)
select * from students limit 0,2;
-- 按照身高从高到矮排序,查找出所有女性,并且分页显示,每页显示2条数据
select * from students where gender=2 order by high desc limit 0,2;

(十)关联查询(连接查询)(多表查询)

1、交叉连接(cross join)(不常用)

MariaDB [ren]> select * from t1;
+------+-------+
| t1id | t1str |
+------+-------+
| 1 | a |
| 2 | b |
| 3 | c |
+------+-------+
3 rows in set (0.00 sec)

MariaDB [ren]> select * from t2;
+------+-------+
| t2id | t2str |
+------+-------+
| 2 | c |
| 3 | d |
+------+-------+
2 rows in set (0.00 sec)

MariaDB [ren]> select * from t1,t2;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 1 | a | 2 | c |
| 1 | a | 3 | d |
| 2 | b | 2 | c |
| 2 | b | 3 | d |
| 3 | c | 2 | c |
| 3 | c | 3 | d |
+------+-------+------+-------+
6 rows in set (0.00 sec)

MariaDB [ren]> select * from t1 cross join t2;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 1 | a | 2 | c |
| 1 | a | 3 | d |
| 2 | b | 2 | c |
| 2 | b | 3 | d |
| 3 | c | 2 | c |
| 3 | c | 3 | d |
+------+-------+------+-------+
6 rows in set (0.00 sec)

-- 多张表连接起来
select * from t1 cross join t2 cross t3;

2、内连接(内关联)(inner join (on))

可以理解为交集(拥有相同元素)

MariaDB [ren]> select * from t1,t2 where t1.t1id=t2.t2id;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 2 | b | 2 | c |
| 3 | c | 3 | d |
+------+-------+------+-------+
2 rows in set (0.00 sec)

MariaDB [ren]> select * from t1 inner join t2 on t1.t1id=t2.t2id;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 2 | b | 2 | c |
| 3 | c | 3 | d |
+------+-------+------+-------+
2 rows in set (0.00 sec)

-- inner join … on
-- 两个表连接查询
select * from students inner join classes
-- 查询能够对应班级的学生以及班级信息
select * from students inner join classes on students.cls_id=classes.id;
-- 按照要求显示姓名,班级
select students.*, classes.name from students inner join classes on students.cls_id=classes.id;
-- 给数据表起名字
select s.name, c.name from students as s inner join classes as c on s.cls_id=c.id;
-- 查询 有能够对应班级的学生以及班级信息,显示学生的所有信息,只显示班级名称
select students.*, classes.name from students inner join classes on students.cls_id=classes.id;
-- 在以上查询中将班级姓名显示在第一列
select classes.name,students.* from students inner join classes on students.cls_id=classes.id;
--关联查询
-- 查询有能够对应班级的学生以及班级信息,按照班级进行排序
select classes.id, students.* from students inner join classes on students.cls_id=classes.id order by classes.id;
-- 当是同一个班级的时候,按照学生的id从小到大
select classes.id, students.* from students inner join classes on students.cls_id=classes.id order by classes.id, students.id;

3、自关联(自连接)

自连接就是把同一张表当做两张表连接起来

创捷一个新表并往表内写数据:

create table areas(
aid int primary key auto_increment,
name varchar(20),
pid int
);

--省份
insert into areas(aid,name,pid) values(1,'北京市',null);
insert into areas(aid,name,pid) values(0,'天津市',null);
insert into areas(aid,name,pid) values(0,'河北省',null);
insert into areas(aid,name,pid) values(0,'山西省',null);
--地级市
insert into areas(aid,name,pid) values(0,'海淀区',1);
insert into areas(aid,name,pid) values(0,'滨海区',2);
insert into areas(aid,name,pid) values(0,'沧州市',3);
insert into areas(aid,name,pid) values(0,'大同市',4);
insert into areas(aid,name,pid) values(0,'朝阳区',1);
insert into areas(aid,name,pid) values(0,'武清区',2);
insert into areas(aid,name,pid) values(0,'石家庄',3);
insert into areas(aid,name,pid) values(0,'太原市',4);
--县级市
insert into areas(aid,name,pid) values(0,'西二旗',5);
insert into areas(aid,name,pid) values(0,'大港',6);
insert into areas(aid,name,pid) values(0,'任丘市',7);
insert into areas(aid,name,pid) values(0,'清徐',8);
insert into areas(aid,name,pid) values(0,'中关村',5);
insert into areas(aid,name,pid) values(0,'汉沽',6);
insert into areas(aid,name,pid) values(0,'河间市',7);
insert into areas(aid,name,pid) values(0,'阳曲',8);

-- 查询出河北省所有市
select * from areas as province inner join areas as city on province.aid=city.pid having name='河北省';
select province.name,city.name from areas as province inner join areas as city on province.aid=city.pid having province.name='河北省';

-- 子查询
-- 标量子查询
-- 查询出北京市所有区的信息
select * from areas where pid=(select aid from areas where name='北京市');
select * from areas where pid in (select aid from areas where name='北京市');

4、外连接(left join,right join)

“外连接”分为两种,“左连接”(left outer join)和“右连接”(right outer join):

左连接:

左侧的表中不符合连接条件的记录也会被展示出来,由于右侧表中并没有可与之连接的记录,所以右侧表中使用“空记录”与左侧表中不符合连接条件的记录进行连接。

右连接同理

--左关联,以左边表为基准,条件对应不上的显示null
select * from classes left join students on students.cls_id=classes.id;
--右关联,以后边为基准,条件对应不上的显示null
select * from classes right join students on students.cls_id=classes.id;

5、联合查询:union与union all

语法格式:select columu_name(s) from table_name1 UNION select columu_name(s) from table_name2

当使用union连接两个查询语句时,两个语句查询出的字段数量必须相同,否则无法使用union进行联合查询。

MariaDB [ren]> select * from t1 union select * from t2;
+------+-------+
| t1id | t1str |
+------+-------+
| 1 | a |
| 2 | b |
| 3 | c |
| 2 | c |
| 3 | d |
+------+-------+
5 rows in set (0.00 sec)

两张表的记录完全相同的话,使用union查询出的重复结果会被合并为一条

使用union all 进行联合查询时,可以将所有内容显示出来,且不会合并重复行

6、全连接(full join)

我们使用"left join"、"union"、"right join"的组合可以实现所谓的“全连接”。

MariaDB [ren]> select * from t1 left join t2 on t1id=t2id;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 2 | b | 2 | c |
| 3 | c | 3 | d |
| 1 | a | NULL | NULL |
+------+-------+------+-------+
3 rows in set (0.00 sec)

MariaDB [ren]> select * from t1 right join t2 on t1id=t2id;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 2 | b | 2 | c |
| 3 | c | 3 | d |
| NULL | NULL | 4 | e |
+------+-------+------+-------+
3 rows in set (0.00 sec)

MariaDB [ren]> select * from t1 left join t2 on t1id=t2id
-> union
-> select * from t1 right join t2 on t1id=t2id;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 2 | b | 2 | c |
| 3 | c | 3 | d |
| 1 | a | NULL | NULL |
| NULL | NULL | 4 | e |
+------+-------+------+-------+
4 rows in set (0.00 sec)
MariaDB [ren]> select * from t1 left join t2 on t1id=t2id where t2id is null
-> union
-> select * from t1 right join t2 on t1id=t2id where t1id is null;
+------+-------+------+-------+
| t1id | t1str | t2id | t2str |
+------+-------+------+-------+
| 1 | a | NULL | NULL |
| NULL | NULL | 4 | e |
+------+-------+------+-------+
2 rows in set (0.01 sec)