（1） DDL, DML, DQL, DCL and common data types

One .MySql

1.MySQL Is a relational database management system
2. Relational database management system , Relational databases store data in different tables , Instead of putting it in a warehouse , This increases the speed , Increased flexibility
3. Small volume 、 Fast 、 The cost is low , Open source

Two .mysql Common data types in databases

2.1 Character type

2.2 value type

2.3 Time type

3、 ... and .DDL、DML、DQL、DCL What are the differences

3.1 DDL( Data definition language ): The relationship between database and database tables

3.1.1 Creating databases and tables

1. grammar :
 create table  Table name (
   Name   data type ( length ),
    Name   data type ( length ),
     Name   data type ( length ),
      Name   data type ( length ) 
     ......... );

2.
 Example ： Create a student table  sid sname sex sage sbirthday date
create table student(
 sid int(11), sname varchar(20),
  sex char(2), sage int(4), 
  sbirthday date 
  );


3. Be careful :
A.  When creating a table   You need to add an English semicolon after the brackets   Columns are separated by commas  
 There is no need to write a comma for the last column name 
B.  The length of the data type of the column   You don't specify   However, it is generally recommended to specify its length 

3.1.2 Modify the name of the table

1. grammar ： alter table Original table name rename to The new name of the table

3.1.3 Delete table

1. grammar : drop table Table name

3.2 DML( Data manipulation language ): Add data 、 Delete 、 Modify the operating . The commonly used statement keywords are INSERT、UPDATE、DELETE etc.

3.2.1 Add data

1. grammar : insert into Table name values( data 1, data 2, data 3);
INSERT INTO student VALUES(1,“ Hehaipeng ”,“123456”,‘2018-11-20’);
.
.2. grammar : insert into Table name ( Name , Name , Name )values( data , data , data );
INSERT INTO student(sid,spwd,sbrithday)VALUES(2,“123”,‘2019-11-23’)
.

Insert multiple data
insert into Table name values( data 1, data 2, data 3),( data 1, data 2, data 3)
insert into Table name ( Name , Name , Name )values( data , data , data ),( data , data , data );
Example ：
INSERT INTO student(sid,spwd,sbrithday)VALUES(3,“122”,‘2019-10-23’), (4,“345”,‘2019-10-23’)
INSERT INTO student VALUES(5,“ Wu Qilong ”,“123456”,‘2018-11-20’),(6,“ Li Ying Hwan ”,“123456”,‘2018-11-20’)

Be careful ：
A. The value of the inserted data must be consistent with the data type in the database list
B. The length of the inserted data value should be less than the length defined in the list
C. Strings can be decorated with single quotation marks and double quotation marks The time type can only be decorated with single quotation marks

3.2.2 Modifying data

1. grammar :update Table name set Name = value , Name = value where Conditions
2. UPDATE student SET sname =“ Brother Mao ” ,spwd=“123” WHERE sid =1;
.
3. When performing modification It needs to be modified according to the conditions

3.2.3 Delete data

grammar :delete from Table name where Conditions
DELETE FROM student WHERE sid=1;

3.3DQL( Data query language ): It is mainly used to query data . Common keywords are SELECT、FROM、WHERE etc.

3.4DCL( Data control language ): It is mainly used to set / Change database user permissions . Common keywords are GRANT、REVOKE etc.