Basic operations on database tables

 1. Create table
 CREATE TABLE TEST 
(
  ID NUMBER(16) NOT NULL
, USERID VARCHAR(30) 
, TITLE VARCHAR(30)
, PROBLEMIDS VARCHAR(30) 
, PRACTICETIME VARCHAR(30) , ANSWERS
VARCHAR(30)
, CREATETIME DATE 
, PRIMARY KEY (ID) -- set the primary key
);
COMMENT ON COLUMN TEST.ID IS 'Exercise Id';


COMMENT ON COLUMN TEST.USERID IS 'User Id';


COMMENT ON COLUMN TEST.TITLE IS 'Exercise title';


COMMENT ON COLUMN TEST .PROBLEMIDS IS 'Problem Id Collection';


COMMENT ON COLUMN TEST.PROBLEMIDS IS 'Problem Id Collection';


COMMENT ON COLUMN TEST.PRACTICETIME IS 'Practice Duration';


COMMENT ON COLUMN TEST.CREATETIME IS 'Practice Time';


2. Drop table
Drop table table name


3. Modify the data type of the attributes of the


table alter table table name modify field name type;


4. Create a sequence


CREATE SEQUENCE emp_sequence --emp_sequence sequence name
     INCREMENT BY 1 -- add several  
     START WITH 1 each time -- start counting from 1  
     NOMAXVALUE -- do not set the maximum value  
     NOCYCLE -- keep accumulating, do not loop  
     CACHE 10;  


5. Add table attributes


Alter table table name add new attribute name add new attribute data type 
Example: Alter table book add price integer(10) null


6 .Delete an attribute in the
table alter table table name drop column column name