Sword refers to data warehouse-SQL01

1. The last course review

Two, two, MySQL syntax one (create database && user && show processlist && kill process)

• 2.1, MySQL field type (numeric type && string type && date type)
• 2.2, SQL type in MySQL && create table && set Unique_key
• 2.3, table building specifications
• 2.4, the character set in MySQL
• 2.5, data addition, deletion, modification, check && matters needing attention

3. Interview questions && homework for this course

1. The last course review

• https://blog.csdn.net/SparkOnYarn/article/details/104876632
• Soft connection (software upgrade, log migration), log migration scenario, the disk burst, move the data of the 50G hard disk to the 2T hard disk, and ln -s makes the soft connection.

Second, MySQL syntax one (create database && user && show processlist && kill process)

1. Create Database && User:

    create database ruozedata;
    grant all privileges on *.* to 'root'@'%' identified by '960210';
    flush privileges;
   

• For us, in big data, tables are the most used, and other developers use the rest of the views, indexes, and stored procedures.
  

2. Kill process in MySQL, log in using terminal

    1、命令行不能带有密码，否则history查看会有泄露
    hadoop:mysqladmin:/usr/local/mysql:>mysql -u root -p960210
    mysql>
    hadoop:mysqladmin:/usr/local/mysql:>mysql -u root -p 960210
    Enter password: 
   
    2、show processlist;		查看正在运行的进程：
    mysql> show processlist;
    +----+------+--------------------+-----------+---------+------+----------+------------------+
    | Id | User | Host               | db        | Command | Time | State    | Info             |
    +----+------+--------------------+-----------+---------+------+----------+------------------+
    |  9 | root | 122.96.50.84:35845 | ruozedata | Sleep   |  716 |          | NULL             |
    | 10 | root | 122.96.50.84:36362 | NULL      | Sleep   |  692 |          | NULL             |
    | 14 | root | localhost          | NULL      | Query   |    0 | starting | show processlist |
    +----+------+--------------------+-----------+---------+------+----------+------------------+
    3 rows in set (0.00 sec)
   
    3、因为此时我们正在使用海狸连接，我们断开dbeaver连接，再次查看进程发现已经少了两个进程了。
    mysql> show processlist;
    +----+------+-----------+------+---------+------+----------+------------------+
    | Id | User | Host      | db   | Command | Time | State    | Info             |
    +----+------+-----------+------+---------+------+----------+------------------+
    | 14 | root | localhost | NULL | Query   |    0 | starting | show processlist |
    +----+------+-----------+------+---------+------+----------+------------------+
    1 row in set (0.00 sec)
   
    4、kill id杀掉进程
    mysql> kill 15;
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> kill 16;
    Query OK, 0 rows affected (0.00 sec)
   
    5、注意：看时间，找到哪个消耗时间长的，有可能导致mysql的服务夯住，别导致锁死 --》 这个SQL的目的一定要搞清楚，到底能不能被kill掉。
   

2.1, MySQL field type

1. Value type:

Types of	Definition
int	Integer
long	Long
double	Double precision
float	Single precision
decimal	Decimal value (linked to amount)

2. String type:

Types of	Definition
char	Fixed length, 0-255 bytes, such as an English letter a, it will automatically fill up 255 bytes when it takes up storage, wasting storage space
varchar	Variable length, string, storage 0-65535 bytes, such as an English letter b, how much storage space it takes up

3. Date type:

Types of	Definition
date	Date type, YYYY-MM-DD
time	Time HH: MM: SS
datetime	Year, month, day, hour, minute, and second, YYYY-MM-DD HH: MM: SS
timestamp	Year, month, day, hour, minute, and second, YYYY-MM-DD HH: MM: SS

Assignment: What is the difference between datetime and timestamp?

2.2, SQL type in MySQL & create data table

DDL: create drop data definition language
DML: insert update delete select Add delete and change check, data operation language
DCL: grant data control language

1、规范的创建rzdata数据表，关键最后5行
create table rzdata(
id int(10) not null auto_increment,			//id不为空自增长
name varchar(30),
age int(3),
createuser varchar(200),							
createtime timestamp not null default current_timestamp,					//创建时间不为空且默认为当前时间
updateuser varchar(200),
updatetime timestamp not null default current_timestamp on update current_timestamp,			//修改时间也不为空，当数据那一刹那发生改变就会留下一个记录时间。
primary key (id)		//id做主键
);

2、数据准备：
insert into ruozedata.rzdata(name,age,createuser,updateuser) values ('john',24,'sail','sail')

3、测试对这条数据进行更新：
update ruozedata.rzdata set age=18 where name='john';

• Modify the age of john to 18, there will be a record:
  

2. Set the unique constraint of name so that data with the same name cannot be inserted:
graphical interface operation:

• Open the layer by layer, click on the constraint, right-click to create a new constraint, select the name field, set it to unique_key, click OK, there is a save in the lower corner, you need to click to execute.
  

insert into ruozedata.rzdata(name,age,createuser,updateuser) values ('john',24,'sail','sail');

insert into ruozedata.rzdata(name,age,createuser,updateuser) values ('john',25,'fox','fox');
出现错误提示：
SQL 错误 [1062] [23000]: Duplicate entry 'john' for key 'rzdata_un'

//下次遇见这个错误就应该能够明白：是设置了唯一值，所以值不能被重复。

• Every data of J head office has createuser, updateuser and upadatetime,

2.3, MySQL table building specification

a. The table name and field name cannot be Chinese or Pinyin; a unified style is needed
. b. A unified style: for example, when you build a table, you need to see what the style of the existing table is: take a field creator as For example, there are many ways to write: create_user, cuser, createuser; if you are not sure, you can take a leader check.
When the time comes, the style of the new project is by you. For
example: take the creation time as an example: ctime, createtime, cretime, cre_time, create_time;
c. The first field of the MySQL table is id self-increase, set as the primary key, it is It doesn't make sense; for mysql to be able to perform high-performance queries.
d. A table can only have one primary key: primary key ==> id, the primary key field must be unique, unique + not null
e. The last four fields need to be added: createuser, createtime, updateuser, updatetime; whether this record is Whether to add or modify is intuitive and clear.
f. Double-click "Column" under the table, and then pull to the end, there will be a comment column, add the comment, intuitively understand the meaning of each field, and finally click Save.

Interview question: Comparison of self-increasing primary key and UUID method

2.4, MySQL character set

1. Show the table-building statement for creating a database. The character set was not set when the database was created. The default setting is the latin character set:

• show create database ruozedata;
• CREATE DATABASE ruozedata /*!40100 DEFAULT CHARACTER SET latin1 */

// The database database has a character set, the table table has a character set, and the column column also has a character set.

2. The server also has a character set:

• show variables like ‘%char%’;

    character_set_client	utf8
    character_set_connection	utf8
    character_set_database	latin1
    character_set_filesystem	binary
    character_set_results	
    character_set_server	latin1
    character_set_system	utf8
    character_sets_dir	/usr/local/mysql-5.7.11-linux-glibc2.5-x86_64/share/charsets/
  

2.5, MySQL addition, deletion and modification check

insert into ruoedata.rzdata(name,age,createuser,updateuser) values (‘john’,24,‘root’,‘root’);

select * from ruozedata.rzdata;

update ruozedata.rzdata set age = 19 where name = ‘john’;

delete from ruozedata.rzdata where name = ‘john’;

Note: Remember not to use * in production, write a limit 10;

select * from rzdata; // Remember to write sql in production and do not add *
select id, name, age from rzdata;

• In the financial system, delete from rzdata without the where condition will cause all data to be deleted; restore it through the binlog file (arch / mysql-bin).

In the future, whether it is update or delete, do not add where conditions, 1 or more data, createtime> = '2019-01-01 00:00:00'

Example: The data table has 100 million data, select * will result in failure to provide external services, select id, name, age from rzdata limit 3; Use limit 10 to view sample data

How does MySQL work in production:

• MySQL's master-slave replication, the master library in production should do write operations as much as possible, and the slave library performs write operations.
• Business ERP APP-> MySQL on server A: write-> data will be automatically synchronized to MySQL on server B: read; this is called read-write separation.
• Confirm clearly where to use select and delete.

3. Interview questions && homework for this course

Interview questions

1. What is the difference between datetime and timestamp?

2. What should I do if the id self-growth primary key is exceeded?

3. What is ENGINE = InnoDB? What is the difference with MyISAM

operation

1. Create a MySQL table specification

2. Sort out DDL and DML statements and execute them in sequence

3. Organize the three sentences, modify the password, grant permissions, refresh permissions