1. Create a table
//Create a student table create table student( ID number(6), //student number NAME varchar2(25), //name BIRTH date, //birthday GRADE number(3,1) //The maximum integer part of the grade is 3 digits, and the decimal part is 1 digit ) //The second way to create a table, use the columns in the existing table as a new table //Create some columns in the student1 table into a new table create table student as select id,name,age from student1 where 1=2 //Indicates that the created table is an empty table, if this condition is not added, the data in the existing table will also be added to the new table
2. Add a column to the created table
//Add the AGE column to the student table alter table student add (AGE number(2) default 18) //The default is 18 years old
3. Modify the column
alter table student modify (ID number(8)) //modify the number of digits in the ID column to 8, if there is data in the table, it cannot be modified
Fourth, delete the column
alter table student drop column AGE //delete the AGE column
5. Rename the column
alter table student rename column ID to IDCARD //Rename the column ID to IDCARD
6. Clear the table
//Clear the data in the student table truncate table student
7. Annotation comments
(1) Add a comment to the specified table
-- Add comments to the table comment on table TABLENAME is 'table comment';
(2) Add a comment to the specified column of the specified table.
-- Add comments to the columns comment on column TABLENAME.COLUMNNAME is 'specified table specified column comment';
(3) Related Views
USER_TAB_COMMENTS DBA_TAB_COMMENTS ALL_TAB_COMMENTS USER_COL_COMMENTS DBA_COL_COMMENTS ALL_COL_COMMENTS
如：select * from user_tab_comments where table_name = 'student';
Eight, TRUNCATE, DELETE, DROP put together to compare:
TRUNCATE TABLE: delete content, release space but not delete the definition (table structure).
DELETE TABLE: Deleting content does not delete the definition (table structure) and does not release space.
DROP TABLE: Deletes content and definitions (table structure), freeing up space.