常用sql commands

1. mysql -uroot -p

2. show databases;

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| ccpdev             |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

3.exit;

4. create database intrepid_detectives; // 创建新的database

5. use intrepid_detectives; // 开始使用新创的那个数据库

database stores their data in tables.数据库将数据保存在table中，一个database可以有多张表,就像一个execel spreadsheet可以有多个sheet一样的概念。

6. show tables;

mysql> use intrepid_detectives;
Database changed
mysql> show tables;
Empty set (0.00 sec)
mysql> use mysql
Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| engine_cost               |
| event                     |
| func                      |
| general_log               |
| gtid_executed             |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| innodb_index_stats        |
| innodb_table_stats        |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| server_cost               |
| servers                   |
| slave_master_info         |
| slave_relay_log_info      |
| slave_worker_info         |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
31 rows in set (0.00 sec)

从上面可以看出mysql默认builtin database内置有很多table

Every table has a set of columns, 每一张表都有一系列的columns(列).每一列都有一个name和一个datatype(at least).

7. create table <name> (<col-name> <col-type>,<col-name> <col-type>)

mysql> use intrepid_detectives;
Database changed
mysql> create table investigations (
    -> title varchar(100),
    -> detective varchar(30),
    -> daysToSolve integer);
Query OK, 0 rows affected (0.04 sec)

mysql> show tables;
+-------------------------------+
| Tables_in_intrepid_detectives |
+-------------------------------+
| investigations                |
+-------------------------------+
1 row in set (0.00 sec)

8. explain investigations; // 可以列出table的结构来：

mysql> explain investigations;
+-------------+--------------+------+-----+---------+-------+
| Field       | Type         | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| title       | varchar(100) | YES  |     | NULL    |       |
| detective   | varchar(30)  | YES  |     | NULL    |       |
| daysToSolve | int(11)      | YES  |     | NULL    |       |
+-------------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

9. insert into investigations values("Finnigan‘s Falut","Carlotta McOwen", 4); //插入一行

table中的每一个entry被称为record. 一个table可以有多个records.  intersection of a column and a record is a field.

10. insert into investigations(datasToSolve, title,detective) values(3, "The Missing Tree", "Finch Hosky"); // 插入一行数据时，指定字段名称，不和数据库表中的字段顺序一致的办法

mysql> insert into investigations values("Finnigan‘s Falut","Carlotta McOwen", 4);
Query OK, 1 row affected (0.00 sec)
mysql> insert into investigations(daysToSolve, title,detective) values(3, "The Missing Tree", "Finch Hosky");
Query OK, 1 row affected (0.00 sec)

11. select * from investigations; // 从investigations表中获取所有数据

mysql> select * from investigations;
+------------------+-----------------+-------------+
| title            | detective       | daysToSolve |
+------------------+-----------------+-------------+
| Finnigan‘s Falut | Carlotta McOwen |           4 |
| The Missing Tree | Finch Hosky     |           3 |
| ohter ing Tree   | sssf            |           3 |
| ohter ing Tree   | sssf            |        NULL |
+------------------+-----------------+-------------+
4 rows in set (0.00 sec)

NULL is the SQL value for "no value";任何一个字段都可能是NULL，只要你不给他赋值！

12. select title, detective from investigations; // 只选择部分字段

13. data types:

  • varchar(100) create table person(name varchar(100));
  • text              create table email(body text);
  • Numbers       int/integer: create table person(age integer unsigned);  // 正整数ff
  • unsigned int: 0-4294967295
  • BIGINT
  • SMALLINT
  • MEDIUMINT
  • TINYINT
  • decimal(precision, scope)比如decimal(10,0)=>0123546789; decimal(5,2)=>123.45;decimal(9,7)=>89.1234567
  • auto_increment: 如果不给这个字段一个明确的值，则自动增1 create table student id integer auto_increment);
  • date,time,datetime
  • date: ‘YYYY-MM-DD‘;
  • time: ‘[H]HH:MM:SS‘
  • datetime: ‘YYYY-MM-DD HH:MM:SS‘ create table order(order_date date);
  • Booleans: bool/boolean: tinyint(1) create table order(fulfilled boolean); 0: false, no-0 is true
  • default values:

create table order(coupon varchar(10) default "nodiscount", customer_id integer default null, datetime datetime default current_timestamp,fulfilled boolean NT NULL default 0);

每一个数据库table都必须有一个primary key, a column that quniquely identifies each row. it can ndeve be null  and must be set on record creation and never changed.

14. 创建constraint (主键)

mysql> create table detectives (
    -> id int not null auto_increment,
    -> name varchar(100),
    -> phone_number varchar(10),
    -> certificationDate date,
    -> constraint detectives_pk primary key (id));
Query OK, 0 rows affected (0.05 sec)

mysql> explain
    -> detectives;
+-------------------+--------------+------+-----+---------+----------------+
| Field             | Type         | Null | Key | Default | Extra          |
+-------------------+--------------+------+-----+---------+----------------+
| id                | int(11)      | NO   | PRI | NULL    | auto_increment |
| name              | varchar(100) | YES  |     | NULL    |                |
| phone_number      | varchar(10)  | YES  |     | NULL    |                |
| certificationDate | date         | YES  |     | NULL    |                |
+-------------------+--------------+------+-----+---------+----------------+
mysql> insert into detectives(name,phone_number,certificationDate)
    -> values("zhangsan",12333,"2002-01-03");
Query OK, 1 row affected (0.00 sec)

mysql> select * from detectives;
+----+----------+--------------+-------------------+
| id | name     | phone_number | certificationDate |
+----+----------+--------------+-------------------+
|  1 | zhangsan | 12333        | 2002-01-03        |
+----+----------+--------------+-------------------+
1 row in set (0.00 sec)

15. alter table investigations rename cases; // 修改表格名称

mysql> alter table investigations rename cases;
Query OK, 0 rows affected (0.01 sec)

mysql> show tables;
+-------------------------------+
| Tables_in_intrepid_detectives |
+-------------------------------+
| cases                         |
| detectives                    |
+-------------------------------+
2 rows in set (0.00 sec)

mysql>

16. alter table cases add criminal varchar(100) // 增加一列, drop criminal则删除一列

mysql> alter table cases add criminal varchar(100);
Query OK, 4 rows affected (0.04 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from cases;
+------------------+-----------------+-------------+----------+
| title            | detective       | daysToSolve | criminal |
+------------------+-----------------+-------------+----------+
| Finnigan‘s Falut | Carlotta McOwen |           4 | NULL     |
| The Missing Tree | Finch Hosky     |           3 | NULL     |
| ohter ing Tree   | sssf            |           3 | NULL     |
| ohter ing Tree   | sssf            |        NULL | NULL     |
+------------------+-----------------+-------------+----------+
4 rows in set (0.00 sec)

17. alter table detectives change certificationDate certification_date date //更改 old certificationDate字段名称为new: certificate_date，type不变!!

mysql> alter table detectives change certificationDate certification_date date;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain detectives;
+--------------------+--------------+------+-----+---------+----------------+
| Field              | Type         | Null | Key | Default | Extra          |
+--------------------+--------------+------+-----+---------+----------------+
| id                 | int(11)      | NO   | PRI | NULL    | auto_increment |
| name               | varchar(100) | YES  |     | NULL    |                |
| phone_number       | varchar(10)  | YES  |     | NULL    |                |
| certification_date | date         | YES  |     | NULL    |                |
+--------------------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

18. alter table cases add id int not null;

alter table cases add primary key (id); // 注意这时由于id默认为0，多个record都具有相同的id，因此这条命令会失败！！！

mysql> select * from cases;
+------------------+-----------------+-------------+----+
| title            | detective       | daysToSolve | id |
+------------------+-----------------+-------------+----+
| Finnigan‘s Falut | Carlotta McOwen |           4 |  0 |
| The Missing Tree | Finch Hosky     |           3 |  0 |
| ohter ing Tree   | sssf            |           3 |  0 |
| ohter ing Tree   | sssf            |        NULL |  0 |
+------------------+-----------------+-------------+----+
4 rows in set (0.00 sec)

mysql> alter table cases add primary key (id);
ERROR 1062 (23000): Duplicate entry ‘0‘ for key ‘PRIMARY‘

解决方案：需要手工或者程序将该列的值更改为不同的整数，随后才能够成功

下面是手工修正id为不同值后能够正确执行add prmiary key(id)和change id id int not null auto_increment的过程

mysql> select * from cases;
+------------------+-----------------+-------------+----+
| title            | detective       | daysToSolve | id |
+------------------+-----------------+-------------+----+
| Finnigan‘s Falut | Carlotta McOwen |           4 |  1 |
| The Missing Tree | Finch Hosky     |           3 |  2 |
| ohter ing Tree   | sssf            |           3 |  3 |
| ohter ing Tree   | sssf            |        NULL |  4 |
+------------------+-----------------+-------------+----+
4 rows in set (0.00 sec)

mysql> alter table cases add primary key(id);
Query OK, 4 rows affected (0.04 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> explain cases;
+-------------+--------------+------+-----+---------+-------+
| Field       | Type         | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| title       | varchar(100) | YES  |     | NULL    |       |
| detective   | varchar(30)  | YES  |     | NULL    |       |
| daysToSolve | int(11)      | YES  |     | NULL    |       |
| id          | int(11)      | NO   | PRI | NULL    |       |
+-------------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> alter table cases change id id INT NOT NULL AUTO_INCREMENT;
Query OK, 4 rows affected (0.04 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> explain cases;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| title       | varchar(100) | YES  |     | NULL    |                |
| detective   | varchar(30)  | YES  |     | NULL    |                |
| daysToSolve | int(11)      | YES  |     | NULL    |                |
| id          | int(11)      | NO   | PRI | NULL    | auto_increment |
+-------------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

19. delete from criminals; // 删除整个criminals表格的数据

mysql> select * from criminals
    -> ;
+-----------+
| name      |
+-----------+
| crimianl1 |
| crimianl2 |
| crimianl3 |
+-----------+
3 rows in set (0.00 sec)

mysql> delete from criminals;
Query OK, 3 rows affected (0.00 sec)

mysql> select * from criminals;
Empty set (0.00 sec)
时间： 2024-10-10 12:22:51

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