DELETE FROM student WHERE grade IS NULL;

一、數據庫操作部分
1.?向?student?表中添加一條新記錄：

INSERT INTO student (id, name, grade) VALUES (1, 'monkey', 98.5);

2.?向?student?表中添加多條新記錄：

INSERT INTO student (id, name, grade) VALUES 
(2, 'bob', 95.5),
(3, 'john', 90.0),
(4, 'smith', 88.5);

3.?向?student?表中添加一條新記錄，只插入?id?和?name?字段，假設?grade?字段可以為NULL或者有默認值：

INSERT INTO student (id, name) VALUES (5, 'jone');DEFAULT 0

4.?更新表，將?grade?大于90的記錄加0.5：

UPDATE student SET grade = grade + 0.5 WHERE grade > 90;

5.?刪除成績為空的記錄（假設成績為空指的是NULL）：

DELETE FROM student WHERE grade IS NULL;

二、用戶權限部分
1.?創建用戶?test1?并設置權限：

CREATE USER 'test1'@'localhost' IDENTIFIED BY 'password';
GRANT SELECT ON student TO 'test1'@'localhost';

2.?查詢用戶?test1?的權限：

SHOW GRANTS FOR 'test1'@'localhost';

3.?刪除用戶?test1?：

DROP USER 'test1'@'localhost';