mysql清空一个表中所有数据

mysql清空一个表中所有数据

• mysql清空一个表中所有数据

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mysql清空一个表中所有数据

TRUNCATE TABLE name

TRUNCATE和DELETE清空数据表的区别

TRUNCATE TABLE 在功能上与不带 WHERE 子句的 DELETE 语句相同：二者均删除表中的全部行。但 TRUNCATE TABLE 比 DELETE 速度快，且使用的系统和事务日志资源少。

DELETE 语句每次删除一行，并在事务日志中为所删除的每行记录一项。TRUNCATE TABLE 通过释放存储表数据所用的数据页来删除数据，并且只在事务日志中记录页的释放。

TRUNCATE TABLE 删除表中的所有行，但表结构及其列、约束、索引等保持不变。新行标识所用的计数值重置为该列的种子。如果想保留标识计数值，请改用 DELETE。如果要删除表定义及其数据，请使用 DROP TABLE 语句。

对于由 FOREIGN KEY 约束引用的表，不能使用 TRUNCATE TABLE，而应使用不带 WHERE 子句的 DELETE 语句。由于 TRUNCATE TABLE 不记录在日志中，所以它不能激活触发器。

TRUNCATE TABLE 不能用于参与了索引视图的表。

示例

下例删除 authors 表中的所有数据。

TRUNCATE TABLE authors

权限

TRUNCATE TABLE权限默认授予表所有者、sysadmin固定服务器角色成员、db_owner 和 db_ddladmin 固定数据库角色成员且不可转让。

练习题

1、 查询Student表中的所有记录的Sname、Ssex和Class列。

select sname,ssex,class from student;

2、 查询教师所有的单位即不重复的Depart列。

select depart from teacher GROUP BY depart;

3、 查询Student表的所有记录。

select * from student;

4、 查询Score表中成绩在60到80之间的所有记录。

select * from score where degree between 60 and 80;

5、 查询Score表中成绩为85，86或88的记录。

select * from score where degree in(85,86,88);

6、 查询Student表中“95031”班或性别为“女”的同学记录。

select * from student where class=95031 or ssex='女';

7、 以Class降序查询Student表的所有记录。

select * from student order by class desc;

8、 以Cno升序、Degree降序查询Score表的所有记录。

select * from score order by cno asc,degree desc;

9、 查询“95031”班的学生人数。

select count(sno) from student where class=95031;

10、查询Score表中的最高分的学生学号和课程号。（子查询或者排序）

select sno,cno,degree from score where degree=(select max(degree) from s
                              core);

11、 查询每门课的平均成绩。

select cno,avg(degree) from score GROUP BY cno

12、查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。

 select * from score where cno like '3%';

13、查询分数大于70，小于90的Sno列。

select sno,degree from score where degree>70 and degree <90;

14、查询所有学生的Sname、Cno和Degree列。

SELECT student.sname,score.cno,score.degree FROM student,score WHERE student.sno=score.sno;

15、查询所有学生的Sno、Cname和Degree列。

SELECT student.sno,student.sname,score.degree from student,score WHERE student.sno=score.sno;

16、查询所有学生的Sname、Cname和Degree列。

SELECT 
student.sname,course.cname,score.degree FROM student,course,score WHERE student.sno=score.sno and score.cno=course.cno;

17、查询“95033”班学生的平均分。

SELECT class,avg(score.degree)  FROM score,student
WHERE student.class= 95033 and student.sno=score.sno;

18、 假设使用如下命令建立了一个grade表：

create table grade(low int(3),upp int(3),rank char(1))
insert into grade values(90,100,’A’)
insert into grade values(80,89,’B’)
insert into grade values(70,79,’C’)
insert into grade values(60,69,’D’)
insert into grade values(0,59,’E’)

现查询所有同学的Sno、Cno和rank列。

SELECT sno,cno,rank from score,grade WHERE degree BETWEEN low and upp;

19、查询选修“3-105”课程的成绩高于“109”号同学成绩的所有同学的记录。

SELECT *
FROM student
WHERE sno in (
SELECT sno
from score
WHERE degree > (
select degree
from score
WHERE sno = '109' and cno = '3-105')
and cno = '3-105');

20 选了多门课程并且是这个课程下不是最高分的

select *
from score
where sno in (select sno from score group by sno having count(sno) > 1)
and degree not in (select max(degree) from score group by cno);

21、查询成绩高于学号为“109”、课程号为“3-105”的成绩的所有记录。

select *
from score
where degree > (select degree
from score
where sno = 109 and cno = '3-105'
);

23、查询“张旭“教师任课的学生成绩。

select course.cname, score.degree
from teacher,
     course,
     score
where teacher.tname = '张旭'
and teacher.tno = course.tno
and score.cno = course.cno;

24、查询选修某课程的同学人数多于5人的教师姓名。

select *
from teacher
where tno =
(select tno
from course
where cno =
(select cno
from score
group by cno
having count(*) > 5));

25、查询95033班和95031班全体学生的记录。

select *
from student
where class in (95033, 95031);

26、 查询存在有85分以上成绩的课程Cno。

select cno, degree
from score
where degree > 85;

27、查询出“计算机系“教师所教课程的成绩表。

select *
from score
where cno in (select cno
from course
where tno in (select tno
from teacher
where depart = '计算机系'
)
);

28、查询“计算 机系”与“电子工程系“不同职称的教师的姓名Tname和职称Prof。

select tname,prof
from teacher;

29、查询选修编号为“3-105“课程且成绩至少高于选修编号为“3-245”的同学的Cno、Sno和Degree,并按Degree从高到低次序排序。

create view show_score_sno_3_105 as
select *
from score
where cno = '3-105';
create view show_score_sno_3_245 as
select *
from score
where cno = '3-245';



select *
from show_score_sno_3_105,
     show_score_sno_3_245
where show_score_sno_3_105.sno = show_score_sno_3_245.sno
and show_score_sno_3_105.degree > show_score_sno_3_245.degree
order by show_score_sno_3_105.degree desc
;

30、查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的Cno、Sno和Degree。

select Cno, Sno, Degree
from Score a
where (select Degree from Score b where Cno = '3-105' and b.Sno = a.Sno) > #查询科目为3-105 的成绩
(select Degree from Score c where Cno = '3-245' and c.Sno = a.Sno) # 查询科目为3-245 的成绩

31、 查询所有教师和同学的name、sex和birthday。

select sname, ssex, sbirthday
from student
union
select tname, tsex, tbirthday
from teacher;

32、查询所有“女”教师和“女”同学的name、sex和birthday。

select teacher.tname,student.sname,teacher.tbirthday, student.sbirthday
from teacher,student where teacher.tsex='女' and student.ssex='女';

33、 查询成绩比该课程平均成绩低的同学的成绩表。

select *
from score
where degree < (select avg(degree) from score);

34、 查询所有任课教师的Tname和Depart。

select tname, depart
from teacher
where tno in (select tno
from course
where cno in (select distinct (course.cno)
from course,
                                 score
where course.cno = score.cno));

35 、查询所有未讲课的教师的Tname和Depart。

select tname,depart
from teacher
where tno not in (select tno
from course
where cno in (select distinct (course.cno)
from course,
                                 score
where course.cno = score.cno));

36、查询至少有2名男生的班号。

select class,count(sno)
from student where ssex='男' GROUP BY class;

37、查询Student表中不姓“王”的同学记录。

select *
from student
where sname not like '王%';

38、查询Student表中每个学生的姓名和年龄。

select sname,
year(now()) - year(Sbirthday)
as '年龄'
from student;

39、查询Student表中最大和最小的Sbirthday日期值。

select max(sbirthday), min(sbirthday)
from student;

40、以班号和年龄从大到小的顺序查询Student表中的全部记录。

select *
from student order by class desc ,sbirthday asc ;

41、查询“男”教师及其所上的课程。

select course.cname,teacher.tname
from course,
     teacher
where teacher.tsex = '男'
and teacher.tno =course.tno;

42、查询最高分同学的Sno、Cno和Degree列。

select sno, cno, degree
from score
where degree = (select max(degree) from score);

43、查询和“李军”同性别的所有同学的Sname。

select sname
from student
where ssex = (select ssex
from student
where sname = '李军');

44、查询和“李军”同性别并同班的同学Sname。

select sname
from student
where ssex = (select ssex
from student
where sname = '李军')
and class = (select class
from student
where sname = '李军');

45、查询所有选修“计算机导论”课程的“男”同学的成绩表。

select *
from score
where cno = (select cno
from course
where cname = '计算机导论') 
and sno in (select sno
from student
where ssex = '男');

select sname
from student
where ssex = (select ssex
from student
where sname = '李军')
and class = (select class
from student
where sname = '李军');

45、查询所有选修“计算机导论”课程的“男”同学的成绩表。

select *
from score
where cno = (select cno
from course
where cname = '计算机导论') 
and sno in (select sno
from student
where ssex = '男');