MySQL practice: 2 Table definition and SQL classification

The definition of the table

Table is a structured file , Can be used to store specific types of data , Such as ： Student information 、 Course information, etc , Can be put in the table , In addition, tables have specific names , B. it cannot be repeated . There are several concepts in the table ： Column 、 That's ok 、 Primary key .

1. Column （ Field ）

Column , Usually do fields , Each field contains ： Field name 、 Field data type 、 Field constraints 、 Field length ;

2. That's ok （ Record ）

That's ok , Usually do the records in the table . The data in the table is by row （ Record ） Stored , There can be 0 Multiple records of a ring ;

SQL The classification of

1. Database query language （DQL）

Represent keyword ：select

2. Database operation language （DML）

Represent keyword ：insert、delete 、update Respectively represents increase 、 Delete 、 Change the data in the table

3. Database definition language （DDL）

Represent keyword ：create、drop、alter Each represents the creation of 、 Delete 、 Modify the structure of the table

4. Transaction control language （TCL）

Represent keyword ：commit、rollback

5. Data control language （DCL）

Represent keyword ：grant、revoke

Be careful ：DML Is to modify the data in the database table , and DDL Is to modify the structure of the data table ;