CREATE TABLE user_tbl(name VARCHAR(20), signup_date DATE);
INSERT INTO user_tbl(name, signup_date) VALUES('张三', '2013-12-22');
UPDATE user_tbl set name = '李四' WHERE name = '张三';
DELETE FROM user_tbl WHERE name = '李四' ;
ALTER TABLE user_tbl ADD email VARCHAR(40);
ALTER TABLE user_tbl ALTER COLUMN signup_date SET NOT NULL;
ALTER TABLE user_tbl RENAME COLUMN signup_date TO signup;
ALTER TABLE user_tbl DROP COLUMN email;
ALTER TABLE user_tbl RENAME TO backup_tbl;
DROP TABLE IF EXISTS backup_tbl;