数据库基本操作语句

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//查看所有数据库
SHOW  DATABASES;
//选择使用数据库
USE blog;
//查看所有表
SHOW TABLES;
//创建表，若存在则删除原表
DROP TABLE  IF EXISTS usertest;
CREATE TABLE usertest(
    id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    NAME VARCHAR(20) NOT NULL,
    age INT CHECK (age>20),
    sex01 ENUM('男','女') DEFAULT '男',
    PASSWORD VARCHAR(50) NOT NULL,
    role VARCHAR(20) NOT NULL DEFAULT 'user' CHECK(role IN('user', 'admin'))
) 
//默认插入表所有数据
INSERT INTO usertest VALUES
    (7,"yto01",15,"男","111","admin"),
    (4,"yto01",15,"男","111","user"),
    (5,"yto01",15,"男","111","admin"),
    (6,"yto01",15,"男","111","user");
//选择插入表数据    
INSERT INTO usertest(NAME,age,PASSWORD) VALUES("yto01",30,"111")
//查询所有
SELECT * FROM usertest
//按条件查询
SELECT NAME AS 姓名,
    age AS 年龄,
    sex01 AS 性别
FROM usertest
WHERE id>2
GROUP BY NAME
HAVING age>15
ORDER BY age
//更新
UPDATE usertest
SET PASSWORD="123"
WHERE age="15"
//删除操作
DELETE FROM usertest
WHERE id=1;
//添加列
ALTER TABLE usertest
ADD COLUMN datetest VARCHAR(20) 
//删除列
ALTER TABLE usertest
DROP COLUMN datetest