SQL不更新表也将旧表添加到新表

Question

it's my first time using SQL, I've followed the syntax but it doesnt work..

use cw312;
CREATE TABLE pet (
name VARCHAR(20),
owner VARCHAR(20),
species VARCHAR(20),
sex CHAR(1),
birth DATE,
death DATE
);
Insert into pet values ('Fluffy','Harold','cat','f','1993-03-04',NULL),
('Claws','Gwen','cat','m','1994-03-17',NULL),
('Buffy','Harold','dog','f','1989-05-13',NULL),('Fang','Benny','dog','m','1990-08-      27',NULL),
('Bowser','Diane','dog','m','1998-08-31','1999-07-11'),
('Chirpy','Gwen','bird','f','1998-09-11',NULL),
('Whistler','Gwen','bird','f','1997-12-09',NULL),
('Slim','Benny','snake','m','1996-04-29',NULL),
('Puffball','Diane','hamster','f','1999-03-30',NULL),
('Daddy', 'Jennifer', 'dog', 'm', '1970-03-30', NULL),
('Major', 'Margaret','cat', 'm', '1993-03-30','2000-04-30');

UPDATE pet SET species = 'dog'
WHERE owner = 'Margaret';




DESCRIBE pet;
SELECT 
  *
FROM
pet;

Why doesnt the update pet set species = dog where owner = margaret update the species to dog?

Also every time i execute this, sql like remakes the Database and adds it to my previous version.. any idea why?

Answer 1

Once table is created and data is inserted, it stay there unless you remove it explicitly.

Do a commit; after the update (and the insert) and then select * from pet;.

Do not rerun the create table or insert statement...

Answer 2

To avoid repeatedly creating the table it helps to do

CREATE TABLE IF NOT EXISTS pet
..

Your initialisation code should be in a separate file really, as every time you run that script the CREATE statement will fail but the INSERT will succeed again and again. Also your table could do with a unique identifier to ensure that 2 pets named 'Fluffy' aren't confused.

Also if you really want to clean out the table, add a TRUNCATE TABLE command just after the create.