02|Oracle learning (data type, DDL)

1. Data type:

• Usually: character type, numeric type, date type, and large field type
• Large field type: store large data and files.
  
  
  When storing large data, basically blob is enough.

2. DDL (Database Definition Language)

• It mainly includes the operation of creating, deleting and modifying database objects.
• DDL operation:
  • Create
  • Drop (delete)
  • Alter (Modify)

2.1 create create data table syntax

2.1.1 Case demonstration

  CREATE TABLE "TB_STUDENTS" (	
    "STU_NUM" CHAR(5) NOT NULL ENABLE, 
	"STU_NAME" VARCHAR2(10) NOT NULL ENABLE, 
	"STU_SEX" CHAR(1) NOT NULL ENABLE, 
	"STU_AGE" NUMBER(2,0), 
	"STU_TEL" CHAR(11)
   ) ;

2.2 Use the Alter statement to modify the data table

2.2.1 Adding columns

• Add a stu_email column to the tb_students table:

ALTER TABLE tb_students ADD stu_email char(50);

2.2.2 Modify the column (here demonstrates modifying the type in the column and changing it to varchar)

• Modify the type in stu_email in the tb_students table:

ALTER TABLE tb_students MODIFY stu_email varchar2(60);

2.2.3 Delete column

• Delete the stu_email column in the tb_students table:

ALTER TABLE tb_students DROP COLUMN stu_email;

2.3 Use the DROP statement to delete the data table

• Delete the student information table tb_students:

DROP TABLE tb_students;

2.4 Delete table data & delete data table

• Delete table data, delete the data stored in the data table, and retain the structure of the data table
  • Truncate table table_name
  • delete [from] table_name
• Delete the data table, delete the table structure (the data in the table will also be deleted at the same time)
  • Drop table table_name