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SQL Server 2016 learning record - Data Definition

2022-07-28 10:24:00 【Hard work Zhang Zhang】

Learning goals ：

1、 Definition and deletion of patterns
2、 The definition of the basic table 、 Delete and modify
3、 data type
4、 Index creation and deletion
5、 The data dictionary

Learning content ：

1、 Definition and deletion of patterns

Defining patterns

--[ example 3.1] Define a student - Course model S-T
create schema "S-T" authorization test;
/* For the user test Defines a pattern S-T*/
-- If not specified < Schema name >, that < Schema name > Implied as < user name >

The definition schema actually defines a namespace .
In this space, you can define the database objects that the schema contains , For example, the basic table 、 View 、 Index, etc. .
stay CREATE SCHEMA It is acceptable that CREATE TABLE,CREATE VIEW and GRANT Clause , Therefore, you can create tables while creating patterns 、 View etc. .

--[ example 3.3] For the user ZHANG A pattern is created TEST, And define a table in it TAB1
CREATE SCHEMA AAA AUTHORIZATION test 
CREATE TABLE TAB1   ( COL1 SMALLINT, 
                      COL2 INT,
                      COL3 CHAR(20),
                      COL4 NUMERIC(10,3),
                      COL5 DECIMAL(5,2)
                      );

Delete the pattern
DROP SCHEMA < Schema name > <CASCADE|RESTRICT>
CASCADE( cascade )： Delete the schema and delete all database objects in the schema
RESTRICT( Limit )： If a subordinate database object is defined in the schema （ As shown in the table 、 View etc. ）, The delete statement is rejected . Only when there are no subordinate objects in this mode can

--[ example 3.4]
DROP SCHEMA s1 CASCADE;
/* Delete the pattern ZHANG, At the same time, the tables defined in the schema TAB1 Also deleted */

2、 The definition of the basic table 、 Delete and modify

Define the base table

--[ example 3.5]  establish “ Student ” surface Student. Student number is the main code , The name value is unique 
CREATE TABLE Student          
      (Sno   CHAR(9) PRIMARY KEY,                                           /*  Column level integrity constraints ,Sno It's the main code */                  
        Sname CHAR(20) UNIQUE,             /* Sname Take unique value */
        Ssex    CHAR(2),
        Sage   SMALLINT,
        Sdept  CHAR(20)
      );

-- [ example 3.6 ]  Build a “ Course ” surface Course
CREATE TABLE  Course
          (Cno       CHAR(4) PRIMARY KEY,
           Cname  CHAR(40),            
           Cpno     CHAR(4),               	                      
           Ccredit  SMALLINT,
           FOREIGN KEY (Cpno) REFERENCES  Course(Cno) 
          );

--[ example 3.7]  Build a “ Students' course selection ” surface SC
CREATE TABLE  SC
    (Sno  CHAR(9),
    Cno  CHAR(4),  
    Grade    SMALLINT,
    PRIMARY KEY (Sno,Cno),  
                    /*  The main code consists of two properties , Must be defined as table level integrity */
    FOREIGN KEY (Sno) REFERENCES Student(Sno),
                /*  Table level integrity constraints ,Sno It's the outside code , The reference table is Student */
    FOREIGN KEY (Cno) REFERENCES Course(Cno)
                /*  Table level integrity constraints , Cno It's the outside code , The reference table is Course*/
	);

Modify the basic table
ALTER TABLE < Table name >
[ ADD[COLUMN] < New column names > < data type > [ Integrity constraints ] ]
[ ADD < Table level integrity constraints >]
[ DROP [ COLUMN ] < Name > [CASCADE| RESTRICT] ]
[ DROP CONSTRAINT< Integrity constraint name >[ RESTRICT | CASCADE ] ]
[ALTER COLUMN < Name >< data type > ] ;

--[ example 3.8]  towards Student Table increase “ Admission time ” Column , Its data type is date type 
ALTER TABLE Student ADD  S_entrance DATE;
/* Whether or not there is data in the basic table , All newly added columns are null  */

--[ example 3.9]  The data type of age is changed from character type to character type （ Suppose the original data type is character type ） Change it to an integer .
ALTER TABLE Student ALTER COLUMN Sage INT;

--[ example 3.10]  Add the constraint that the course name must be unique .
ALTER TABLE Course ADD UNIQUE(Cname);

Delete base table
DROP TABLE < Table name >［RESTRICT| CASCADE］;
RESTRICT： There are restrictions on deleting tables .
The base table to be deleted cannot be referenced by constraints of other tables
If there are objects that depend on the table , The table cannot be deleted
CASCADE： There are no restrictions on deleting this table .
While deleting the base table , Related dependent objects are deleted together

--[ example 3.11]  Delete Student surface 
DROP TABLE  Student  CASCADE ;
/* The basic table definition is deleted , Data is deleted   Index built on table 、 View 、 Triggers, etc. will generally be deleted  */

3、 data type

Character data type