Mysql database - general syntax DDL DML DQL DCL

Catalog

Data model

General grammar and classification

DDL（ Data definition language ）

Database operation

Table operations - Inquire about

  Table operations - establish

Table operations - modify

Table operations - Delete  

Table operations - data type

DML（ Data operation language ）

DML Introduce

DML Add data

DML Modifying data

DML Delete data

DQL（ Data query language ）

grammar ：

Basic query

Conditions of the query

Aggregate query （ Aggregate functions ） 

Group query

  Sort query

Paging query

DQL Execution order

DCL（ Data control language ）

Manage users

Access control

---

Data model

database   A warehouse for storing data , Data is organized and stored   DataBase（DB）

Database management system   Large software for manipulating and managing databases   DataBase Management System（DBMS）

SQL  Programming language for operating relational databases , A set of unified standards for operational relational database are defined ,（SQL）

General grammar and classification

Relational database （RDBMS) 

Concept :

Based on the relational model , A database consisting of multiple interconnected two-dimensional tables .

characteristic ：
1. Use tables to store data , use the same pattern , Easy to maintain

2. Use sQL Language operation , Unified standards , Easy to use  
 

SQL General grammar

1.SQL Statements can be written in one or more lines , It ends with a semicolon .

2. SQL Statements can use spaces / Indent to enhance the readability of the statement .

3.MySQL Database SQL Statement is case insensitive , It is recommended to use uppercase .

4. notes :
Single-line comments :-- Note content or # The comment (MySQL specific )
Multiline comment :/* The comment */

• DDL: Data definition language , Used to define database objects （ database 、 surface 、 Field ）
• DML: Data operation language , It is used to add, delete and modify the data in the database table
• DQL: Data query language , Used to query the records of tables in the database
• DCL: Data control language , Used to create database users 、 Control the control permissions of the database

DDL（ Data definition language ）

Database operation

Query all databases ：

SHOW DATABASES;

Querying the current database ：

SELECT DATABASE();

Create database ：

CREATE DATABASE [ IF NOT EXISTS ] Database name [ DEFAULT CHARSET Character set ] [COLLATE Sort rule ];

Delete database ：

DROP DATABASE [ IF EXISTS ] Database name ;

Using a database ：

USE Database name ;

matters needing attention

• UTF8 The character set length is 3 byte , Some symbols account for 4 byte , So I recommend utf8mb4 Character set

Table operations - Inquire about

Query all tables in the current database ：

SHOW TABLES;

Query table structure ：

DESC Table name ;

Query the table creation statement of the specified table ：

SHOW CREATE TABLE Table name ;

  Table operations - establish

CREATE TABLE  Table name (
     Field 1  Field 1 type  [COMMENT  Field 1 notes ],
     Field 2  Field 2 type  [COMMENT  Field 2 notes ],
     Field 3  Field 3 type  [COMMENT  Field 3 notes ],
    ...
     Field n  Field n type  [COMMENT  Field n notes ]
)[ COMMENT  Table annotation  ];

Be careful ： There is no comma after the last field  

Be careful :[...] Is an optional parameter , There is no comma after the last field
 

Table operations - modify

Add fields ：

ALTER TABLE Table name ADD Field name type ( length ) [COMMENT notes ] [ constraint ];
example ：ALTER TABLE emp ADD nickname varchar(20) COMMENT ' nickname ';

Change data type ：

ALTER TABLE Table name MODIFY Field name New data types ( length );

Modify the field name and field type ：

ALTER TABLE Table name CHANGE Old field name new field name type ( length ) [COMMENT notes ] [ constraint ];
example ： take emp Tabular nickname Change the field to username, The type is varchar(30)
ALTER TABLE emp CHANGE nickname username varchar(30) COMMENT ' nickname ';

Table operations - Delete  

Delete field ：

ALTER TABLE Table name DROP Field name ;

Modify the name of the table ：

ALTER TABLE Table name RENAME TO The new name of the table

Delete table ：

DROP TABLE [IF EXISTS] Table name ;

Delete table , And recreate the table ：

TRUNCATE TABLE Table name ;

Note when deleting a table , All data in the table will also be deleted

Table operations - data type

DDL- Table operations - data type
MysQL There are many data types in , It is mainly divided into three categories : value type 、 String type 、 Date time type .
 

 

 

  An example of adding, deleting, and modifying a query

mysql> use itcast;
Database changed
mysql> create table tb_user(
    -> id int comment ' Number ',
    -> name varchar(50) comment ' full name ',
    -> age int comment ' Age ',
    -> gender varchar(1) comment ' Gender '
    -> ) comment ' User table ';
Query OK, 0 rows affected (0.03 sec)

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

mysql> desc tb_user;
+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| id     | int         | YES  |     | NULL    |       |
| name   | varchar(50) | YES  |     | NULL    |       |
| age    | int         | YES  |     | NULL    |       |
| gender | varchar(1)  | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> show create table tb_user;
+---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                                                                                                                                                                      |
+---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tb_user | CREATE TABLE `tb_user` (
  `id` int DEFAULT NULL COMMENT ' Number ',
  `name` varchar(50) DEFAULT NULL COMMENT ' full name ',
  `age` int DEFAULT NULL COMMENT ' Age ',
  `gender` varchar(1) DEFAULT NULL COMMENT ' Gender '
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT=' User table ' |
+---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> create table emp(
    -> id int comment ' Number ',
    -> workno varchar(10) comment ' Job number ',
    -> name varchar(10) comment ' full name ',
    -> gender char(1) comment ' Gender ',
    -> age tinyint unsigned comment ' Age ',
    -> idcard char(18) comment ' ID number ',
    -> entrydate date comment ' Entry time '
    -> ) comment ' The employee table ';
Query OK, 0 rows affected (0.11 sec)

mysql> desc emp
    ->
    -> desc emp
    -> desc emp;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'desc emp
desc emp' at line 3
mysql> desc emp;
    -> desc emp;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'desc emp' at line 2
mysql>
mysql>  create table emp(
    ->     -> id int comment ' Number ',
    ->     -> workno varchar(10) comment ' Job number ',
    ->     -> name varchar(10) comment ' full name ',
    ->     -> gender char(1) comment ' Gender ',
    ->     -> age tinyint unsigned comment ' Age ',
    ->     -> idcard char(18) comment ' ID number ',
    ->     -> entrydate date comment ' Entry time '
    ->     -> ) comment ' The employee table ';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-> id int comment ' Number ',
    -> workno varchar(10) comment ' Job number ',
    -> n' at line 2
mysql>
mysql> desc emp;
+-----------+------------------+------+-----+---------+-------+
| Field     | Type             | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| id        | int              | YES  |     | NULL    |       |
| workno    | varchar(10)      | YES  |     | NULL    |       |
| name      | varchar(10)      | YES  |     | NULL    |       |
| gender    | char(1)          | YES  |     | NULL    |       |
| age       | tinyint unsigned | YES  |     | NULL    |       |
| idcard    | char(18)         | YES  |     | NULL    |       |
| entrydate | date             | YES  |     | NULL    |       |
+-----------+------------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

mysql> alter table emp add nickname varchar(20) comment ' nickname ';
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> desc emp;
+-----------+------------------+------+-----+---------+-------+
| Field     | Type             | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| id        | int              | YES  |     | NULL    |       |
| workno    | varchar(10)      | YES  |     | NULL    |       |
| name      | varchar(10)      | YES  |     | NULL    |       |
| gender    | char(1)          | YES  |     | NULL    |       |
| age       | tinyint unsigned | YES  |     | NULL    |       |
| idcard    | char(18)         | YES  |     | NULL    |       |
| entrydate | date             | YES  |     | NULL    |       |
| nickname  | varchar(20)      | YES  |     | NULL    |       |
+-----------+------------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

mysql>
mysql> alter table emp change nickname username varchar(30) comment ' user name ';
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> desc emp;
+-----------+------------------+------+-----+---------+-------+
| Field     | Type             | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| id        | int              | YES  |     | NULL    |       |
| workno    | varchar(10)      | YES  |     | NULL    |       |
| name      | varchar(10)      | YES  |     | NULL    |       |
| gender    | char(1)          | YES  |     | NULL    |       |
| age       | tinyint unsigned | YES  |     | NULL    |       |
| idcard    | char(18)         | YES  |     | NULL    |       |
| entrydate | date             | YES  |     | NULL    |       |
| username  | varchar(30)      | YES  |     | NULL    |       |
+-----------+------------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

mysql> alter table emp drop username;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc emp;
+-----------+------------------+------+-----+---------+-------+
| Field     | Type             | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| id        | int              | YES  |     | NULL    |       |
| workno    | varchar(10)      | YES  |     | NULL    |       |
| name      | varchar(10)      | YES  |     | NULL    |       |
| gender    | char(1)          | YES  |     | NULL    |       |
| age       | tinyint unsigned | YES  |     | NULL    |       |
| idcard    | char(18)         | YES  |     | NULL    |       |
| entrydate | date             | YES  |     | NULL    |       |
+-----------+------------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

mysql> alter table emp rename to employee;
Query OK, 0 rows affected (0.09 sec)

mysql> desc emp;
ERROR 1146 (42S02): Table 'itcast.emp' doesn't exist
mysql> show table;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1
mysql>
mysql> show tables;
+------------------+
| Tables_in_itcast |
+------------------+
| employee         |
| tb_user          |
+------------------+
2 rows in set (0.00 sec)

mysql>
mysql> drop table if exists tb_user;
Query OK, 0 rows affected (0.09 sec)

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

mysql> truncate table employee;
Query OK, 0 rows affected (0.04 sec)

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

mysql>

Graphical interface tools -DG

DML（ Data operation language ）

DML Introduce

DML The full English name is Data Manipulation Language( Data operation language ), It is used to record the data of tables in the database Additions and deletions operation .

Add data （INSERT)
Modifying data （UPDATE)

Delete data （DELETE)
 

DML Add data

Specified field ：

INSERT INTO Table name ( Field name 1, Field name 2, ...) VALUES ( value 1, value 2, ...);

All fields ：

INSERT INTO Table name VALUES ( value 1, value 2, ...);

Batch add data ：

INSERT INTO Table name ( Field name 1, Field name 2, ...) VALUES ( value 1, value 2, ...), ( value 1, value 2, ...), ( value 1, value 2, ...);
INSERT INTO Table name VALUES ( value 1, value 2, ...), ( value 1, value 2, ...), ( value 1, value 2, ...);

Be careful :
· When inserting data , The specified field order needs to correspond to the order of values one by one .

· String and date data should be enclosed in quotation marks .
· The size of the inserted data , It should be within the specified range of the field .
 

DML Modifying data

Modifying data ：

UPDATE Table name SET Field name 1 = value 1, Field name 2 = value 2, ... [ WHERE Conditions ];

example ：
UPDATE emp SET name = 'Jack' WHERE id = 1;

DML Delete data

Delete data ：

DELETE FROM Table name [ WHERE Conditions ];

DQL（ Data query language ）

grammar ：

1. SELECT
2. Field list
3. FROM
4. Table name field
5. WHERE
6. List of conditions
7. GROUP BY
8. Group field list
9. HAVING
10. List of conditions after grouping
11. ORDER BY
12. Sort field list
13. LIMIT
14. Paging parameters

Basic query

Query multiple fields ：

SELECT Field 1, Field 2, Field 3, ... FROM Table name ;
SELECT * FROM Table name ;

Set alias ：

SELECT Field 1 [ AS Alias 1 ], Field 2 [ AS Alias 2 ], Field 3 [ AS Alias 3 ], ... FROM Table name ;
SELECT Field 1 [ Alias 1 ], Field 2 [ Alias 2 ], Field 3 [ Alias 3 ], ... FROM Table name ;

Remove duplicate records ：

SELECT DISTINCT Field list FROM Table name ;

escape ：

SELECT * FROM Table name WHERE name LIKE '/_ Zhang San ' ESCAPE '/'
/ After that _ Not as a wildcard

Conditions of the query

grammar ：

SELECT Field list FROM Table name WHERE List of conditions ;

Conditions ：

Comparison operator	function
>	Greater than
>=	Greater than or equal to
<	Less than
<=	Less than or equal to
=	be equal to
<> or !=	It's not equal to
BETWEEN … AND …	In a certain range （ Containing minimum 、 Maximum ）
IN(…)	stay in The values in the following list , A commonplace
LIKE Place holder	Fuzzy matching （_ Match a single character ,% Match any character ）
IS NULL	yes NULL

Logical operators	function
AND or &&	also （ Multiple conditions hold at the same time ）
OR or ||	perhaps （ Any one of several conditions holds ）
NOT or !	Not , No

  give an example ：

--  Age equals 30
select * from employee where age = 30;
--  Age is less than 30
select * from employee where age < 30;
--  Less than or equal to 
select * from employee where age <= 30;
--  No ID card 
select * from employee where idcard is null or idcard = '';
--  Have ID card 
select * from employee where idcard;
select * from employee where idcard is not null;
--  It's not equal to 
select * from employee where age != 30;
--  Age 20 To 30 Between 
select * from employee where age between 20 and 30;
select * from employee where age >= 20 and age <= 30;
--  The following statement does not report an error , But I can't find any information 
select * from employee where age between 30 and 20;
--  The gender is female and the age is less than 30
select * from employee where age < 30 and gender = ' Woman ';
--  Age equals 25 or 30 or 35
select * from employee where age = 25 or age = 30 or age = 35;
select * from employee where age in (25, 30, 35);
--  The name is two words 
select * from employee where name like '__';
--  The last ID card is X
select * from employee where idcard like '%X';

Aggregate query （ Aggregate functions ） 

Common aggregate functions ：

function	function
count	Statistical quantity
max	Maximum
min	minimum value
avg	Average
sum	Sum up

grammar ：

SELECT Aggregate functions ( Field list ) FROM Table name ;

example ：
SELECT count(id) from employee where workaddress = " Guangdong province, ";

Group query

grammar ：

SELECT Field list FROM Table name [ WHERE Conditions ] GROUP BY Group field name [ HAVING Filter conditions after grouping ];

where and having The difference between ：

• The timing of execution is different ：where Is to filter before grouping , dissatisfaction where Condition does not participate in grouping ;having Yes, filter the results after grouping .
• Different judgment conditions ：where Aggregate functions cannot be judged , and having Sure .

  Example ：

--  Group by sex , Count the number of men and women （ Show only the number of groups , It doesn't show which is male and which is female ）
select count(*) from employee group by gender;
--  Group by sex , Count the number of men and women 
select gender, count(*) from employee group by gender;
--  Group by sex , Count the average age of men and women 
select gender, avg(age) from employee group by gender;
--  Age is less than 45, And grouped according to the working address 
select workaddress, count(*) from employee where age < 45 group by workaddress;
--  Age is less than 45, And grouped according to the working address , Get the number of employees greater than or equal to 3 My work address 
select workaddress, count(*) address_count from employee where age < 45 group by workaddress having address_count >= 3;

matters needing attention

• Execution order ：where > Aggregate functions > having
• After grouping , The query fields are generally aggregate functions and grouping fields , Querying other fields makes no sense

  Sort query

grammar ：

SELECT Field list FROM Table name ORDER BY Field 1 sort order 1, Field 2 sort order 2;

sort order ：

• ASC: Ascending （ Default ）
• DESC: Descending

give an example ： 

--  Sort in ascending order by age 
SELECT * FROM employee ORDER BY age ASC;
SELECT * FROM employee ORDER BY age;
--  Two field sorting , Sort in ascending order by age , The entry time is sorted in descending order 
SELECT * FROM employee ORDER BY age ASC, entrydate DESC;

matters needing attention

If it is multi field sorting , When the first field has the same value , Will be sorted according to the second field

Paging query

grammar ：

SELECT Field list FROM Table name LIMIT Starting index , Number of query records ;

Example ：

1. -- Query the data on the first page , Exhibition 10 strip
2. SELECT * FROM employee LIMIT 0, 10;
3. -- Check page two
4. SELECT * FROM employee LIMIT 10, 10;

matters needing attention

• Starting index from 0 Start , Starting index = （ Look up the page number - 1） * Each page shows the number of records
• Paging query is the dialect of database , Different databases have different implementations ,MySQL yes LIMIT
• If the query is the first page of data , The starting index can be omitted , Direct abbreviation LIMIT 10

 

DQL Execution order

FROM -> WHERE -> GROUP BY -> SELECT -> ORDER BY -> LIMIT

 

DCL（ Data control language ）

Manage users

Query the user ：

1. USER mysql;
2. SELECT * FROM user;

Create user :

CREATE USER ' user name '@' Host name ' IDENTIFIED BY ' password ';

Change user password ：

ALTER USER ' user name '@' Host name ' IDENTIFIED WITH mysql_native_password BY ' New password ';

Delete user ：

DROP USER ' user name '@' Host name ';

 

--  Create user test, Only on the current host localhost visit 
create user 'test'@'localhost' identified by '123456';
--  Create user test, Can be accessed from any host 
create user 'test'@'%' identified by '123456';
create user 'test' identified by '123456';
--  Change Password 
alter user 'test'@'localhost' identified with mysql_native_password by '1234';
--  Delete user 
drop user 'test'@'localhost';

matters needing attention

• Host name can be used % Pass through

Access control

Common permissions ：

jurisdiction	explain
ALL, ALL PRIVILEGES	All permissions
SELECT	Query data
INSERT	insert data
UPDATE	Modifying data
DELETE	Delete data
ALTER	Modify table
DROP	Delete database / surface / View
CREATE	Create database / surface

For more permissions, see List of permissions

Query authority ：

SHOW GRANTS FOR ' user name '@' Host name ';

Grant authority ：

GRANT Permission list ON Database name . Table name TO ' user name '@' Host name ';

Revoke authority ：

REVOKE Permission list ON Database name . Table name FROM ' user name '@' Host name ';

matters needing attention

• Multiple permissions are separated by commas
• Authorization time , Database name and table name can be * Carry out general matching , On behalf of all

  for example ：

show grants for 'heima'@'%';

grant all on itcast.* to 'heima'@'%';

revoke all on itcast.* from 'heima'@'%';