[Favorites] MySQL 100 commands, all content of basic operations (frequently read and always new)

foreword

Hello everyone, I am Qiu Yilin.

The semester is coming to an end. Before the end, I will summarize an article on MySQL. It has a lot of space and content, so it is a collection-level article, because the content coverage is relatively wide, relatively shallow, and easy to understand. It is very suitable for novices who are learning mysql . It can be used as a msyql command manual Daquan, covering all the basic operations of mysql (I believe you will understand it when you see the directory structure).

Always look new, always look new, always look new! ! ~

Remember to bookmark + pay attention so as not to get lost.

Welcome to the cloud community

1. ER model

The entity-relationship model (ER model for short) provides a user-oriented expression method that is not bound by any DBMS, and is widely used as a data modeling tool in database design.
When we are working on a project, we need to use the ER model to draw the ER diagram in advance, so that the database structure is clear and reasonable.

A constraint in a DBMS that enforces restrictions on the data or types of data that can be inserted, updated, or deleted from a table. The whole purpose of constraints is to maintain data integrity while updating, deleting, inserting into a table.

type of constraint

• not-null, unique, default, validation, key constraints – primary key, foreign key, domain constraint, map constraint

2. Data type

3. Field naming convention

1. It is composed of 26 English letters (case-sensitive) and natural numbers from 0-9 (often not needed) plus an underscore _'. The name is concise and clear, and multiple words are separated by an underscore _'.
2. Generally use lowercase naming.
3. It is forbidden to use database keywords, such as: table, time, datetime, primary, etc.
4. Field names generally use nouns or verb-object phrases, such as user_id, is_good.
5. The name of the field used must be easy to understand, generally no more than three English words.

4. Database creation and management

help

illustrate:

• table_name: data table table name
  col_name: field name
  data_type: data type of the field

View the creation process

grammar:show create 关键字(table database) 名称;

show create table t_teacher;

4.1. Create database

grammar:create database db_name;

create database db_test;

4.2, delete the database

grammar:drop database db_name;

drop database db_test;

4.3. List databases

grammar:show databases;

show databases;

4.4, backup database

If operating on the host machine, the -h parameter can be omitted.

grammar:mysqldump -h 主机名 -u 用户名 -p 密码 数据库名称 > 脚本文件路径;

mysqldump -uroot -p000000 test > test.sql;

4.5. Restoring the database

grammar:mysql -h 主机名 -u 用户名 -p 密码 数据库名称 < 脚本文件路径;

mysql -uroot -p000000 test < test.sql;
或者
source test.sql;

4.6. Using a certain database

grammar:use db_name;

use db_test;

5. Data table creation and management

5.1, create table, structure

Syntax: create table table_name(col_name1 data_type1,col_name2 data_type2,....);
Create a t_test data table, the field is id, name (the number in the data type is the field length)

create table t_test(id char(20),name char(10));

5.2. View table structure

grammar:describe table_name;
desc table_name;

describe can be abbreviated as desc.

describe t_test;
desc t_test;

5.3, view the data table

grammar:show tables;

show tables;

5.4. Copy table structure

If you are copying the table structure of another database, add the name of the database before table_name2

grammar:create table new_table_name1 like old_table_namme2;

Copy the t_test1 table structure in the database db_test to the current database, and name it as the table structure t_test2.

create table t_test1 like t_test2;

5.5. Copy table data

consistent table structure

insert into table_name_new select * from table_name_old;

Inconsistent table structure

insert into table_name_new(column1,column2...) select column1,column2... from table_name_old;

5.6. Modify the table name

grammar:alter table old_table_name （旧名字） rename new_table_name（新名字）;

alter table t_test1 rename t_test2;

5.7. Add fields

grammar:alter table table_name add col_name1（添加字段名）data_type （字段类型）;

alter table t_test add test_address varchar(255);

5.7.1. Put the added field first

grammar:alter table table_name add col_name1（添加字段名）data_type （字段类型） first;

alter table t_test add test_address varchar(255) first;

5.7.2. Put the added field after the test2 field

grammar:alter table table_name add col_name1（添加字段名）data_type （字段类型） after test2(字段);

alter table t_test add test1 varchar(20) after test2;

5.8, delete field

grammar:alter table t_reader drop reader_qq (删除的字段名);

alter table t_test drop test1;

5.9. Modify the data type of the field

Syntax: alter table table_name modify col_name1（字段名） data_type (字段类型);
Change the data type of test2 from varchar to char.

alter table table_name modify test2 char(100);

5.10. Modify the name of the field

grammar:alter table table_name change old_col_name（字段名） new_col_old（新字段名） data_type（字段数据类型);

alter table t_test change test_address  address char(100);

5.11, set the primary key

Role: to ensure the uniqueness of the input record
. Method:

• set when creating the table
• Set after table creation

Syntax: create table table_name(xs_id char(12),xs_name char(10) primary key (xs_id));
When creating the studnet table, set xs_id as the primary key.

create table student (xs_id char(12),xs_name char(10),primary key(xs_id));

When creating studnet table, set xs_id and xs_name as primary key. This way of setting multiple fields as the primary key is called: composite primary key. A composite primary key is also a primary key (uniqueness).

create table student (xs_id char(12),xs_name char(10),primary key(xs_id,xs_name));

5.12, delete the primary key

语法：alter table table_name drop primary key;

alter table studnet drop primary key;

5.13, foreign key

Role: to ensure data integrity. like:

• entity integrity
• User Defined Integrity
• Referential integrity
  Only after a field becomes a primary key can it become a foreign key in another table.
  grammar:alter table table_name add constraint 外键名称 foreign key （设为外键的字段名）references t_table2(主键字段名);

Set the id field in the t_test1 table as the primary key, and the id field in the t_test2 table as the foreign key.

alter table t_test2 add constraint fk1 foreign key (id) references t_test1(id);

5.14. Delete foreign key

Syntax: show create table table_name;
Get the foreign key name:

 show create table t_test2;

grammar:alter table t_test2 drop foreign key 外键名称;

alter table t_test2 drop foreign key fk1;

6. Data update

6.1, insert insert record

6.1.1. Insert a single record

grammar:insert [into] 表名 [字段1,字段n] values(值1,值n);

insert into test values(123,'tt');
insert into test(pid) values(124);

6.1.2. Insert multiple records

insert into test values(125,'ttww'),(126,'ttwwe'),(127,'ttqqq');

6.1.3, sub query, insert multiple records

Use the content field queried by select to insert it into the field corresponding to inert

grammar:insert [into] 表名1 [字段1，字段n] select [字段1,字段n] from 表名2 [where语句];

insert into  test-1 select * from test-2;
insert into  test-1(pid,name) select pid,name from test-2;

6.2, delete delete records

grammar:delete from 表名 [where <条件>];

delete from test; ## 删除所有记录
delete from test where pid==123;   #删除id为123的这条记录。

6.3, update update record

grammar:update 表名 set 列名1 = 值1,列名2 = 值2,…[where 条件];

7. Data query

7.1. Single table query

1. Syntax: select <[列名1，列名n 或通配符 [as 别名] ]> from 表名;
as: alias a field

2. Grammar: select distinct <[列名1，列名n 或通配符]> from 表名;
Remove duplicates, add before the corresponding field

Symbolic expression:

7.1.1, where common keywords

• AND, OR: Connect multiple conditions
  BETWEEN AND: Between
  IS NULL: Query for null values
  ​​IN: Query in a certain set
  LIKE: Fuzzy query

7.1.2. Wildcards

"*" wildcard: match any column name
"_" wildcard: match a single character
"%" wildcard: match any character

7.1.3, order by child clause

You can use the order by clause to install one or more attribute columns (multiple attributes separated by commas) in ascending (ASC) or descending (DESC) order, and the default is ascending.

--查询结果按照bookPrice列值的降序排列
select * from books order by bookPrice desc;

7.1.4. Aggregate functions

example:

#查询book表中年龄最大的
select max(age) from book;

7.1.5, group by child clause

Group the query results by the values ​​of one or more columns, and the values ​​are equal as a group.

select count(*),pressName from books group by pressName;

For example: In the following list, there is 1 name named "People's Posts and Telecommunications Press", and 6 names named "Tsinghua University Press".

7.2. Connection query

Query data according to the relationship between the columns of two tables or multiple tables, that is, join query.

7.2.1. Simple connection

Connection query is actually a data query through the columns related to each other between tables. For relational databases, connection is the most important feature of query.
Simple joins use commas to join two or more tables and are the most commonly used form of multi-table queries.

example:

select b.reader_id,br.book_name from books b,borrow_record br where b.ISBN=br.ISBN;

7.2.2, JOIN connection

In addition to using commas to connect, you can also use JOIN to connect.

7.2.2.1, inner join (inner join)

1) Equivalent connection

select * from books b inner join borrow_record br where b.ISBN=br.ISBN;

2) Unequal connection

select * from books b inner join borrow_record br where b.ISBN<>br.ISBN;

7.2.2.2, outer join (left join, right join)

1) You can also use where to execute conditional judgment after left join on

select * from books b left join borrow_record br on b.ISBN=br.ISBN;

2)
You can also use where to execute conditional judgment after the right connection on

select * from books b right join borrow_record br on b.ISBN=br.ISBN;

7.3. Nested query

In the SQL language, a select-from-where statement is called a query block . Queries that nest one query block within the conditions of another query block's where clause or having phrase are called nested queries .
grammar:select <字段名或通配符> from <表或视图名> where [表达式] (select <字段名或通配符> from <表或视图名> where [表达式] )

7.3.1. Subqueries with IN predicates

select * from books where isbn in (select * isbn from brrowrecord where reader_id='201801');

7.3.2. Subqueries with comparison operators

Refers to the connection between the parent query and the subquery using a comparison operator. You can use comparison operators such as >, <, =, >=, <=, !=, <>, etc.

select * from books where isbn=(select * isbn from brrowrecord where reader_id='201801');

7.3.3. Subqueries with ANY (SOME) or ALL predicates

When a subquery returns a single value, a comparison operator can be used, but when multiple values ​​are returned, the ANY (some systems use SOME) or ALL predicate must be used. When using the ANY or ALL predicate , a comparison operator must be used at the same time .

Predicate interpretation:

Example:

#查询读者编号为"201801"的学生未借阅的所有图书的详细信息；
select * from books where isbn <> all(select isbn from brrowwrecord where reader_id="201801");

7.3.4. Subquery with EXISTS predicate

The subquery of the EXISTS predicate does not return any data and is a Boolean (true or false) logical judgment. After using the existential quantifier EXISTS, if the inner query result is empty, the outer WHERE clause returns true, otherwise it is negated.
example:

#查询读者编号为201801的读者没有借阅过的图书信息
select * from books where not exists (select * from borrowrecord where isbn=books.isbn and reader_id="201801");

7.4. Combine query

#两个表字段合并显示，两个表相同字段合并后显示一次
select * from t_major1 union select * from t_major;

8. Index

An index is a decentralized storage structure created to speed up the retrieval of data rows in a table .

8.1. Create an index for the created table

1) Use the CREATE INDEX method to create an ordinary descending index for its field name stu_id on the already created table t_student.

Syntax: create [unique | fulltext] index index_name on table_name(co_name ase|desc , [co_name ase|desc] )#Multi-field indexes are separated by commas (,)

create index index_student on t_student(stu_id desc)

2) Use the ALTER TABLE...ADD INDEX method to create a full-text index for the field column course_name of the table t_course.

Syntax: alter table table_name add [unique | fulltext] index index_name(co_name ase|desc , [co_name ase|desc] )#Multi-field indexes are separated by commas (,)

alter table t_course add fulltext index index_course_name(course_name)

8.2. Create an index when creating a new table

Create the table t_teacher2, which is consistent with the structure of t_teacher (the table structure cannot be copied), create an index during the table creation process, and create a unique ascending index for teacher_id.

create table t_teacher2(teacher_id char(10),teacher_name char(50),index index_tea_id(teacher_id asc));

9. View

View (View) is actually a table derived from one or more relational tables (or views). It is a virtual table similar to a soft link.

9.1, create a view

Create a view view_basic_info, the data comes from the t_student table
Syntax:create view <视图名> as select_statement

create view view_basic_info as select * from t_student;

9.2, modify the view

grammar:create view <视图名> as select_statement

alter view view_basic_info as select * from t_student;

9.3, delete view

drop view view_basic_info;

10. Stored procedure

The stored procedure is very similar to the function in the program. It can write some code segments that need to be called multiple times to achieve a specific task into a procedure , save it in the database, and call it by the procedure name. These procedures are called for the stored procedure.

DELIMITER Definition: Set the delimiter used after the end of the statement, the default terminator of MYSQL is ";".

10.1. Create a stored procedure

mysql> delimiter $  
mysql> create procedure p1()
    -> comment '读者信息'
    -> begin
    -> select * from t_reader;
    -> end $
mysql> delimiter ;

10.2. Call stored procedure

mysql> call p1;

10.3. Delete stored procedure

mysql> drop procedure p1;

10.4. Create a stored procedure with parameters

10.4.1、in

1. Create a stored procedure with input parameters to query the student information corresponding to a certain student number.

mysql> delimiter $
mysql> create procedure p3(in stuid char(10))
comment "查询某个学号对应的学生信息" 
begin
select * from t_student where stu_id=stuid;
end $
mysql> delimiter ;

mysql> call p3(1631607102); #调用存储过程

10.4.2、out

2. Create a stored procedure with an output parameter to query the number of all students.

Note: Adding @ before the variable name means: session variable
session variable: not limited to the inside of the stored procedure

mysql> delimiter $
mysql> create procedure p6(out stucount int) 
begin 
select COUNT(stu_id) into stucount from t_student; 
end $
mysql> delimiter ;

mysql> call p6(@stucount);  #调用存储过程
mysql> select @stucount;	#查看输出变量

10.4.3、inout

3. Create a stored procedure with input and output parameters to add 20 points to a certain grade.

mysql> delimiter $
mysql> create procedure p9(inout testname int) 
begin 
update t_score set grade=grade+20 where score_id=testname; 
select grade into testname from t_score where score_id=testname; 
end $
mysql> delimiter ;

mysql> set @testname=1001;
mysql> call p9(@testname);
mysql> select @testname;

@pra: session variables are not restricted to inside stored procedures

11. Basics of SQL Programming

11.1, SQL programming basic syntax

SQL is essentially a programming language that requires variables to store data. Many attribute controls in MySQL are implemented through variables in MySQL.

Variables are divided into two categories: system variables and user variables ;

System variables: effective for all users, that is, all clients in MySQL.
User variable: for specifying the corresponding user.

11.1.1. System variables

MySQL system variables are actually used to store system parameters, and are used to initialize and set MySQL’s occupation of system resources, storage locations of configuration files, and so on. Most variables exist as adjustment parameters of the MySQL system, and modifying these parameters will affect the operation mode of MySQL.

System variables: divided into global (global) variables and session (session) variables.

Global variables: affect the overall operation of the entire MySQL instance.
Session variables: affect the current connection to the MySQL instance.

11.1.1.1. View system variables

11.1.1.1.1, session variables and global variables

grammar:show variables 条件语句

Condition statement: represents the filter condition to query the system variable (optional)

View all system variables; session variables first, global variables second.

show variables;  //查看所有系统变量

Limit the scope of system variables through the global and session keywords.

show global variables;  //查看全局变量
show session variables;  //查看会话变量

If you want to view some specific system variables, but not all, you can use like and where statements:

show variables like 'log%';  //查询所有变量名以log开头的系统变量

If in the query, in addition to the variable name condition, the value condition is also used in the condition, you can use the where statement:

show variables where variable_name like 'log%' and value='OFF';

11.1.1.1.2, configuration variables and monitoring variables

MySQL system variables can also be divided into: configuration variables and monitoring variables

show variables;  // 查看配置变量
show status; // 查看监控变量

Similarly, if you want to add conditional statements when querying system status variables, the method is the same as when querying configuration variables.

11.1.1.2, common system variables

In the work, the database is generally divided into "development library", "test library", "online library" and other environments.

View current MySQL version information

mysql> show variables like 'version%';
+-------------------------+------------------------------+
| Variable_name           | Value                        |
+-------------------------+------------------------------+
| version                 | 8.0.30                       |
| version_comment         | MySQL Community Server - GPL |
| version_compile_machine | x86_64                       |
| version_compile_os      | Win64                        |
| version_compile_zlib    | 1.2.12                       |
+-------------------------+------------------------------+
5 rows in set, 1 warning (0.02 sec)

Maximum number of connections

When connecting to the database, you often MySQL: ERROR 1040： Too many connectionsencounter error messages. One situation is that MySQL cannot handle it because of too much access. At this time, the number of 'slave' servers can be increased to ease the pressure of 'reading'. Another situation is that max_connectionsthe value is set too small.

mysql> show variables like 'max_connections';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 200   |
+-----------------+-------+
1 row in set, 1 warning (0.00 sec)

current connections

Only then Threads_connected <= max_connectionscan the normal connection to the database be guaranteed.

mysql> show status like 'Threads_connected';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_connected | 1     |
+-------------------+-------+
1 row in set (0.00 sec)

MySQL encoding configuration information

If the problem of Chinese garbled characters occurs, it is usually caused by inconsistent MySQL encoding settings.

mysql> show variables like '%set%';
+---------------------------------------+---------------------------------------------------------------+
| Variable_name                         | Value                                                         |
+---------------------------------------+---------------------------------------------------------------+
| auto_increment_offset                 | 1                                                             |
| character_set_client                  | utf8mb4                                                       |
| character_set_connection              | utf8mb4                                                       |
| character_set_database                | utf8mb4                                                       |
| character_set_filesystem              | binary                                                        |
| character_set_results                 | utf8mb4                                                       |
| character_set_server                  | utf8mb4                                                       |
| character_set_system                  | utf8mb3                                                       |
| character_sets_dir                    | D:\APP\Pro_Software\MYSQL\mysql-8.0.30-winx64\share\charsets\ |
| innodb_monitor_reset                  |                                                               |
| innodb_monitor_reset_all              |                                                               |
| optimizer_trace_offset                | -1                                                            |
| performance_schema_setup_actors_size  | -1                                                            |
| performance_schema_setup_objects_size | -1                                                            |
| resultset_metadata                    | FULL                                                          |
| transaction_write_set_extraction      | XXHASH64                                                      |
+---------------------------------------+---------------------------------------------------------------+
16 rows in set, 1 warning (0.00 sec)

11.1.1.3. Setting and modifying system variables

For system variables, before the MySQL service starts, we can modify the my.cnf configuration file; or when starting, specify the startup parameters to modify.
After the service is started, the variable value can be modified through the set statement.

//修改全局变量
set global var_name = value;
set @@global.var_name = value;

//修改会话变量
set session var_name = value;
set @@session.var_name = value;

11.1.2. User variables

User variable refers to the variable defined by the user, which can assign a value to the user variable. Statements can be used to set 和 selectdefine assignments (no assignment is empty by default), and the select statement can also view the assigned value.

Variable scope: the session scope of the current connection (if the current connection is disconnected, the previously defined variables will not be accessible).

Define the form of user variables: start with '@', such as: "@var_name", so as to distinguish user variables and column names in the table. You can use '='，':='the operator assignment. If you use the select statement, you must use ':='the operator assignment

grammar:
set @var_name = value1 [ , @var_name = value2];
set @var_name := value1 [ , @var_name := value2];

set statement

mysql> set @test=123;  
Query OK, 0 rows affected (0.00 sec)

mysql> select @test;
+-------+
| @test |
+-------+
|   123 |
+-------+
1 row in set (0.00 sec)


mysql> set @var1=1,@var2=2;
Query OK, 0 rows affected (0.00 sec)

mysql> select @var1,@var2;
+-------+-------+
| @var1 | @var2 |
+-------+-------+
|     1 |     2 |
+-------+-------+
1 row in set (0.00 sec)

select statement

mysql> select @var:=1,@var:=2;
+---------+---------+
| @var:=1 | @var:=2 |
+---------+---------+
|       1 |       2 |
+---------+---------+
1 row in set, 2 warnings (0.00 sec)

mysql> select @var,@var;
+------+------+
| @var | @var |
+------+------+
|    2 |    2 |
+------+------+
1 row in set (0.00 sec)

11.2. SQL system functions

11.2.1, Condition judgment function

if function

Syntax: if(expr1,expr2,expr3)
If the result of the expression is true (Boolean type), then return the value of expr2, otherwise return the value of expr3.

case structure

case case_expr
  when when_value then statement_list
  [ when when_value then statement_list ]...
end case

case_expr: Conditional judgment expression, which determines which when is executed. when_value: Indicates the possible value of the expression. If a when_value value is the same as the result of the case_expr expression value, the statement_list statement after the corresponding then keyword will be executed.

11.2.2. Mathematical functions

A commonly used function. Mainly used to process numbers, including
mathematical functions such as integers and floating point numbers

11.2.3. String functions

String functions are very commonly used functions. Processing for data type data.
string functions

11.2.4. Date function

date function

11.2.5. Aggregate functions

Generally acts on the specified field.
aggregate function

11.3, custom function

If, case, loop, repeat, while, and for statements can be used in functions, please understand this part by yourself.

11.3.1. Create function

grammar:

create function func_name(func_parameter)
returns type
 body

create function: keyword to create a function
func_name: function name
func_parameter: function parameter list, in the form of (param_nae type), such as: (num1 int, num2 int)
type: function return value type, such as: int, char(50) wait.
The general format of the body is as follows:

begin
   retrun(select 查询语句);
end

delimiter delimiter: MySQL's default delimiter is a semicolon ';'. Using the delimiter statement, you can modify the default delimiter

example:

Create a function that queries the age of a reader.

delimiter $ 
create function func_reader_age2(name char(50))
returns int
begin
return(select year(curdate())-year(reader_birthday) from t_reader where reader_name=name);
end $
delimiter ;
select func_reader_age2("肖华");

11.3.2. Delete function

drop function function_name;

12. Trigger

A trigger is a stored procedure that executes automatically in response to a specific event. (Specific events: additions, deletions, and modifications to database tables)
triggers can be defined to be executed automatically before or after INSERT, UPDATE, and DELETE statements change the data table.

12.1, create a trigger

grammar:CREATE TRIGGER trigger_name trigger_time trigger_event ON table_name FOR EACH ROW [trigger_order] trigger_body

Detailed parameter explanation:

trigger_time: The execution time of the trigger: AFTER (after) | BEFORE (before)
trigger_event: The event triggered by the trigger: DELETE | UPDATE | INSERT
FOR EACH ROW: Indicates that the operation on any record that meets the trigger event will trigger the trigger
table_name: the name of the table element trigger event operation table
trigger_body: the SQL statement to create the trigger

(1) Create an Insert trigger. After inserting a record into t_student, insert the table name t_student and the insertion time into the t_log table.

CREATE TABLE t_log  
(logno int AUTO_INCREMENT primary key,    
tname varchar(20),    
logtime datetime);
SELECT * FROM t_log;

create trigger tr_insert after insert on t_student for each row 
insert into t_log (tname,logtime) VALUES('t_student',now());

insert into t_student(stu_id) values("0123456789");
select * from t_student;
select  * from t_log;
 

(2) Create an insert trigger for the t_score1 table. When a piece of data is inserted into the t_score1 table, a record corresponding to stu_id is automatically added in t_student1, and a record corresponding to course_id is automatically added in t_course1e.

create table t_score1 like t_score;
insert into t_score1 select  * from t_score;

//创建触发器
create trigger t_insert3 after insert on t_score1 for each row 
begin
insert into t_student1(stu_id) VALUES("1123456789") ;
insert into t_course1(course_id) VALUES("12345678") ;
end

//验证
insert into t_score1(score_id,stu_id,course_id) values(1018,1631607101,16610001);
select  * from  t_student1 where stu_id = "1123456789";
select  * from  t_course1 where course_id = "12345678";

12.2, view the trigger

show triggers;

12.3. Delete trigger

drop trigger trigger_name;

12.4 Application of NEW and OLD

Two temporary tables, NEW and OLD, are defined in MySQL to save the table before and after the trigger modification for easy reference.

12.4.1. Flowchart

12.4.2. Case

(1) When modifying the birthday of a student in the table t_student1, insert the birthday before modification and the birthday after modification into another table t_backup (need to be created).

//创建触发器
create trigger t_updata1 after update on t_student1 for each row
begin
insert into t_backup(old_birthday,new_birthday) values(old.stu_birthday,new.stu_birthday);
end

//测试
update t_student1 set stu_birthday="1999-12-12" where stu_name="王伟";

(2) When deleting a record in the t_major1 table, insert the deleted record into another table (need to create a new table).

//创建触发器
create trigger t_delete1 after delete on t_major1 for each row
begin
insert into t_major_back values(old.major_id,old.major_name);
end
//测试
delete from t_major1 where major_name="计算机应用技术";

13. Affairs

grammar:

START TRANSACTION | BEGIN
DML语句
COMMIT 或 ROLLBACK

START TRANSACTION, BEGIN: can start a new transaction
DML statement: insert, delete, update
COMMIT, ROLLBACK: define commit, rollback transaction

13.1. Introduction

A transaction is a complete business logic and a unit of work. like:

Assuming a transfer, transfer 10,000 from account A to account B.

• Subtract 10000 from the money in account A (update statement)
  Add 10000 to the money in account B (update statement)

This is a complete business logic. The two updata statement requirements must both succeed or both fail .

Only DML statements will have transactions, and other statements have nothing to do with transactions! ! !

For insert, delete, and update,
only the above three statements are related to the transaction, and nothing else is related.

Therefore, a transaction is a batch of DML statements that succeed or fail at the same time

13.2, commit, rollback transaction

Commit the transaction: commit; statement, which represents the end of the transaction.
Rollback transaction: rollback; statement (rollback can only be rolled back to the last commit point forever!)

13.3, transaction includes 4 characteristics

A (atomic):

Explain that a transaction is the smallest unit of work. Indivisible.

C (Consistency):

All transactions require that in the same transaction, all operations must succeed or fail at the same time to ensure data consistency.

I (isolation) key points:

There is a certain isolation between A transaction and B transaction.
There is a wall between classroom A and classroom B, and this wall is isolation.
When transaction A operates a table, another transaction B also operates this table? ? ?

D (persistence):

A guarantee that a transaction will eventually close. Transaction submission is equivalent to saving data that has not been saved to the hard disk to the hard disk!

13.4. Case

Add 10 points to the C language score of the student whose student ID is "1631607101". If the score after adding 10 points is found to be greater than 100 points, execute the rollback operation of the transaction, otherwise submit the transaction.

mysql> select * from t_score1;
+----------+------------+-----------+-------+
| score_id | stu_id     | course_id | grade |
+----------+------------+-----------+-------+
| 1001     | 1631607101 | 16610001  |    92 |
| 1002     | 1631607101 | 16610002  |    75 |
| 1003     | 1631607101 | 16610003  |    88 |
| 1004     | 1631607102 | 16610004  |   100 |
| 1005     | 1631607102 | 16610005  |    99 |
| 1006     | 1631611104 | 16610003  |    76 |
| 1007     | 1631611104 | 16610004  |   107 |
| 1008     | 1631611104 | 16610005  |    97 |
| 1009     | 1631611104 | 16610006  |    90 |
| 1010     | 1731613106 | 16610009  |    75 |
| 1011     | 1731613107 | 16610009  |    97 |
| 1012     | 1631601101 | 16610002  |    86 |
| 1013     | 1631601102 | 16610003  |    85 |
| 1014     | 1631601103 | 16610004  |    90 |
| 1015     | 1631601104 | 16610005  |    80 |
| 1016     | 1631601105 | 16610006  |    79 |
| 1017     | 1631601105 | 16610007  |    98 |
| 1018     | 1631607101 | 16610001  |  NULL |
+----------+------------+-----------+-------+
18 rows in set (0.00 sec)

mysql> begin;
mysql> update t_score1 set grade=grade+10 where stu_id="1631607101";
mysql> select * from t_score1 where stu_id="1631607101" and grade < 100;
+----------+------------+-----------+-------+
| score_id | stu_id     | course_id | grade |
+----------+------------+-----------+-------+
| 1002     | 1631607101 | 16610002  |    85 |
| 1003     | 1631607101 | 16610003  |    98 |
+----------+------------+-----------+-------+


--回滚后，数据就没有改变
mysql> rollback;  --如果这里换成commit; 代表事务结束。

mysql> select * from t_score1 where stu_id="1631607101" and grade < 100;
+----------+------------+-----------+-------+
| score_id | stu_id     | course_id | grade |
+----------+------------+-----------+-------+
| 1001     | 1631607101 | 16610001  |    92 |
| 1002     | 1631607101 | 16610002  |    75 |
| 1003     | 1631607101 | 16610003  |    88 |
+----------+------------+-----------+-------+
3 rows in set (0.00 sec)

--执行commit;后，就无法回到commit之前，代表事务结束。
mysql> commit;

14. User management and rights management

语法：CREATE USER user_name [IDENTIFIED BY [PASSWORD] “user_password”]

user_name: The created account name, a complete account consists of the user name and the host, in the form of 'user_name'@'localhost'.

14.1. User Management

14.1.1. Create user

1. Default all hosts

create user test_1 identified by '123456';

2. Specify the user's host as localhost

create user test1@localhost identified by '123456';

14.1.2. Modify user password

14.1.3. Delete user

drop user user_name;

14.2. Authority Management

14.2.1. Authorization granted

GRANT priv_type[(column_list)] ON database.table TO user [IDENTIFIED BY [PASSWORD] 'password'] [,user IDENTIFIED BY [PASSWORD] 'password'] ... [WITH with-option['with-option']...]

priv_type: Authorization type (ALL means all permissions).
column_list: Specifies the column name, indicating that the permission acts on those columns, not specifying that it acts on the entire table.
database.table: Specifies the database and table.
user: username, a complete account is composed of username and host, in the form of 'user_name'@'localhost'.
IDENTIFIED BY: Specifies to set a password for the account, and the existing user does not need to specify a password.
password: Indicates the user's new password, and existing users can use no password.
WITH with-option['with-option']: Specifies authorization options.

1. Use the grant statement to create the user soft, the password is 123456, and grant select, insert, update permissions and delegation permissions (grant option) to all tables in all databases

grant select,insert,update on *.* to soft@localhost identified by '123456' with grant option;

2. Use the grant statement and grant select, insert, and update permissions to all tables in all databases

grant select,insert,update on *.* to soft;

14.2.1.1. View permission

grammar:GRANT priv_type[(column_list)] ON [object_type]{table_name | * | *.* | db_name.*} FROM user [,user]...

select * from user;

Ordinary users can also execute

show grants for ‘user'@'host';

14.2.2. Revoking permissions

revoke select,insert,update on *.* from soft@localhost;

15. Backup and restore database

15.1. Backup

grammar:

E:\db_backup>mysqldump
Usage: mysqldump [OPTIONS] database [tables]
OR     mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]
OR     mysqldump [OPTIONS] --all-databases [OPTIONS]
For more options, use mysqldump --help

backup a database

MYSQLDUMP -u user_name -p db_name table_name1 table_name2... > backup_name.sql

user_name: User name
db_name: select the database for backup
table_name: select the table in the backup database
backup_name: the name of the generated backup file

backup multiple databases

MYSQLDUMP -u user_name -p --databases db_name1 db_name2... > backup_name.sql

backup all databases

MYSQLDUMP -u user_name -p --all-databases > backup_name.sql

15.2. Recovery

MYSQL -u user_name -p [db_name] < backup_name.sql

db_name: Used to specify the name of the database. When specifying a database, restore the tables under the database. When not specified, it means to restore all the data in the backup file.

16. Log

Four types of MySQL logs : error log, query log, slow query log, and binary log.
The files corresponding to the four types of logs are stored in the data directory of the mysql data directory. You can use show variablesthe command to view
the error log. The default is enabled, and the other three logs are defaulted to Open.

16.1. Error log

The error log records the error information when the MySQL service starts and stops and runs, such as: the syntax error of the running sql statement.
Error logging is enabled by default and cannot be disabled.

Check if "Error Log" is enabled

--使用show variables命令后可以看到日志文件存放位置：D:\APP\Pro_Software\MYSQL\data\
show variables like "%log_erro%";
+----------------------------+----------------------------------------------------+
| Variable_name              | Value                                              |
+----------------------------+----------------------------------------------------+
| binlog_error_action        | ABORT_SERVER                                       |
| log_error                  | D:\APP\Pro_Software\MYSQL\data\DESKTOP-T92IEER.err |
| log_error_services         | log_filter_internal; log_sink_internal             |
| log_error_suppression_list |                                                    |
| log_error_verbosity        | 2                                                  |
+----------------------------+----------------------------------------------------+
5 rows in set, 1 warning (0.00 sec)

16.2. Query log

The query log records the start and stop information of the MySQL server, client connection information, and SQL statements for adding, deleting, checking and modifying data records .
The query log is turned off by default. Since the query log will record all user operations, if the query log is enabled, it will take up more disk space. It is recommended to define the query log to save disk space.

Check if "Query Log" is enabled

--使用show variables命令后可以看到日志文件存放位置：D:\APP\Pro_Software\MYSQL\data\
mysql> show variables like "%general%";
+------------------+----------------------------------------------------+
| Variable_name    | Value                                              |
+------------------+----------------------------------------------------+
| general_log      | OFF                                                |
| general_log_file | D:\APP\Pro_Software\MYSQL\data\DESKTOP-T92IEER.log |
+------------------+----------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)

--开启
mysql> set global general_log = ON;
Query OK, 0 rows affected (0.00 sec)

--关闭
mysql> set global general_log = OFF;
Query OK, 0 rows affected (0.00 sec)

16.3. Slow query log

Slow logging records various operations that take longer than a specified time to execute .
By analyzing the slow query log, you can effectively locate the performance bottleneck of each MySQL command execution.

Check if "Slow Query Log" is enabled

--使用show variables命令后可以看到日志文件存放位置：D:\APP\Pro_Software\MYSQL\data\
mysql> show variables like "%slow%";
+-----------------------------+---------------------------------------------------------+
| Variable_name               | Value                                                   |
+-----------------------------+---------------------------------------------------------+
| log_slow_admin_statements   | OFF                                                     |
| log_slow_extra              | OFF                                                     |
| log_slow_replica_statements | OFF                                                     |
| log_slow_slave_statements   | OFF                                                     |
| slow_launch_time            | 2                                                       |
| slow_query_log              | OFF                                                     |
| slow_query_log_file         | D:\APP\Pro_Software\MYSQL\data\DESKTOP-T92IEER-slow.log |
+-----------------------------+---------------------------------------------------------+
7 rows in set, 1 warning (0.01 sec)

--开启
mysql> set global slow_query_log=on;
Query OK, 0 rows affected (0.00 sec)

--关闭
mysql> set global slow_query_log = off;
Query OK, 0 rows affected (0.00 sec)


--测试
mysql> select sleep(10);
+-----------+
| sleep(10) |
+-----------+
|         0 |
+-----------+
1 row in set (10.01 sec)

16.4, binary log

The two-level log records various operations of the database in binary form other than queries, also called a change log. It is mainly used to record MySQL statements that modify data or may cause data changes, and record the statement occurrence time, execution time, and operation data .

Check if "binary log" is enabled

--使用show variables命令后可以看到日志文件存放位置：D:\APP\Pro_Software\MYSQL\data\
mysql> show variables like "%log_bin%";
+---------------------------------+---------------------------------------------+
| Variable_name                   | Value                                       |
+---------------------------------+---------------------------------------------+
| log_bin                         | ON                                          |
| log_bin_basename                | D:\APP\Pro_Software\MYSQL\data\binlog       |
| log_bin_index                   | D:\APP\Pro_Software\MYSQL\data\binlog.index |
| log_bin_trust_function_creators | OFF                                         |
| log_bin_use_v1_row_events       | OFF                                         |
| sql_log_bin                     | ON                                          |
+---------------------------------+---------------------------------------------+
6 rows in set, 1 warning (0.00 sec)

--查询binlog文件名
mysql> show master status;
+---------------+----------+--------------+------------------+-------------------+
| File          | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+---------------+----------+--------------+------------------+-------------------+
| binlog.000119 |    57106 |              |                  |                   |
+---------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

Summarize

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