【数据库】SQL练习

有3张表，学生、课程、成绩

t_student:

student_id number(6) 主键,

student_name varchar2(20) 不能重复不能为空,

student_sex varchar2(1) '1'-男 '2'-女，默认为'1'，进行check约束

t_class:

class_id number(6) 主键,

class_name varchar(20) 不能重复不能为空

t_score:

score_id number(6) 主键,

student_id number(6) 外键约束不能为空,如果主表删除了级联删除,

class_id number(6) 外键约束不能为空,如果主表删除了级联删除,

score_score（成绩） number(4,1) 不能为空，最大100分

score_makeup（补考成绩） number(4,1)，-1表示没有进行补考，最大100分

要求：

1、根据上述信息创建3张表

2、t_student表添加1列student_status varchar2(1) '1'-有效 '0'-无效，默认为'1'，进行check约束，要用alter table实现

3、输入一些测试数据，要用insert into语句

4、用1条sql语句查询所有不及格学生的信息，要求显示：学生姓名不及格课程总数

5、用1条sql语句查询男生、女生分别有多少人，要求显示：男生人数女生人数

6、用1条sql语句查询0-10分、11-20分、21-30分、...81-90分、91-100分分别有多少人，要求显示：分数段区间人数

7、查询补考也不及格的学生信息，要求显示：学生姓名课程名称该课成绩该课补考成绩不及格课程总数补考不及格课程总数

--1.创表

/* Table: "t_student" */

/*drop table ttt_student cascade constraints;

create table ttt_student (

student_id number(6) not null,

student_name varchar2(20) unique not null,

student_sex varchar2(1) default 1 check(student_sex='1' or student_sex='2'),

constraint PK_TTT_STUDENT primary key (student_id)

);*/

DROP TABLE TTT_STUDENT CASCADE CONSTRAINTS;--删除关联

CREATE TABLE TTT_STUDENT (

STUDENT_ID NUMBER(6) NOT NULL,

STUDENT_NAME VARCHAR2(20) UNIQUE NOT NULL,

STUDENT_SEX VARCHAR2(1) DEFAULT 1 CHECK(STUDENT_SEX='1' OR STUDENT_SEX='1'),

PRIMARY KEY(STUDENT_ID)

);

/* Table: "t_class" */

/*drop table ttt_class cascade constraints;

create table ttt_class (

class_id number(6) not null,

class_name varchar2(20) unique not null,

constraint PK_TTT_CLASS primary key (class_id)

);*/

DROP TABLE TTT_CLASS CASCADE CONSTRAINTS;

CREATE TABLE TTT_CLASS(

CLASS_ID NUMBER(6) NOT NULL,

CLASS_NAME VARCHAR(20) UNIQUE NOT NULL,

PRIMARY KEY(CLASS_ID)

);

/* Table: "t_score" */

/*alter table ttt_score

drop constraint FK_TTT_SCORE_REFERENCE_TTT_STUDEN;

alter table ttt_score

drop constraint FK_T_SCORE_REFERENCE_T_CLASS;

drop table ttt_score cascade constraints;

create table "t_score" (

"score_id" number(6) not null,

"student_id" number(6) not null,

"class_id" number(6) not null,

"score_score" number(4,1) not null check("score_score" between 0 and 100),

"score_makeup" number(4,1) default -1 check(("score_makeup" between 0 and 100) or "score_makeup"=-1),

constraint PK_T_SCORE primary key ("score_id"),

foreign key ("student_id") references "t_student"("student_id") on delete cascade,

foreign key ("class_id") references "t_class"("class_id") on delete cascade

);*/

ALTER TABLE TTT_SCORE

DROP CONSTRAINT FK_TTT_SCORE_REFERENCE_TTT_STUDENT;

ALTER TABLE TTT_SCORE

DROP CONSTRAINT FK_TTT_SCORE_REFERENCE_TTT_CLASS;

DROP TABLE TTT_SCORE CASCADE CONSTRAINTS;

CREATE TABLE TTT_SCORE(

SCORE_ID NUMBER(6) NOT NULL,

STUDENT_ID NUMBER(6) NOT NULL,

CLASS_ID NUMBER(6) NOT NULL,

SCORE_SCORE NUMBER(4,1) NOT NULL CHECK(SCORE_SCORE BETWEEN 0 AND 100),

SCORE_MAKEUP NUMBER(4,1) DEFAULT -1 CHECK((SCORE_MAKEUP BETWEEN 0 AND 100) or SCORE_MAKEUP = -1),

PRIMARY KEY(SCORE_ID),

FOREIGN KEY(STUDENT_ID) REFERENCE TTT_STUDENT(STUDENT_ID) ON DELETE CASCADE,

FOREIGN KEY(CLASS_ID) REFERENCE TTT_CLASS(CLASS_ID) ON DELETE CASCADE

);

--------------------------------------------------------------------------------

--2.alter加列

--alter table "t_student" add "student_status" number(1) default 1 check("student_status"=1 or "student_status"=0);

/*alter table "t_student" add "student_status" varchar2(1) default 1 check("student_status"='1' or "student_status"='0');*/

ALTER TABLE TTT_STUDENT ADD STUDENT_STATUS VARCHAR2(1) DEFAULT 1 CHECK(STUDENT_STATUS = 1 OR STUDENT_STATUS = 0);

--------------------------------------------------------------------------------

--3.insert加数据，update改数据

insert into "t_student" ("student_id" , "student_name" ) values (1,'dwq');

insert into "t_student" ("student_id" , "student_name" ) values (2,'jtd');

insert into "t_student" ("student_id" , "student_name" ) values (3,'lch');

update "t_student" set "student_sex"='2' where "student_name" ='lch';

insert into "t_class" ("class_id" , "class_name" ) values (1,'math');

insert into "t_class" ("class_id" , "class_name" ) values (2,'english');

insert into "t_score" ("score_id" ,"student_id","class_id","score_score" ) values (1,1,1,100);

insert into "t_score" ("score_id" ,"student_id","class_id","score_score" ) values (2,2,1,55);

insert into "t_score" ("score_id" ,"student_id","class_id","score_score" ) values (3,3,1,59);

insert into "t_score" ("score_id" ,"student_id","class_id","score_score" ) values (4,2,2,55);

update "t_score" set "score_makeup"=59 where "score_id" =2;

update "t_score" set "score_makeup"=33 where "score_id" =3;

update "t_score" set "score_makeup"=21 where "score_id" =4;

update "t_score" set "score_makeup"=80 where "score_id" =4;

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--4.学生姓名不及格课程总数

/*select "t_student"."student_name", count("t_score"."class_id") as "failed"

from "t_student" join "t_score"

on ("t_student"."student_id" = "t_score"."student_id" and "t_score"."score_score" <60)

group by "t_student"."student_name";*/

SELECT TTT_STUDENT.STUDENT

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--5.男生人数女生人数

/*select (case when "student_sex"='1' then 'M' when "student_sex"='2' then 'F' end ) "sex",Count(*) "num" from "t_student"

group by "student_sex";*/

select sum(decode("student_sex",'1',1)) boy_sum,sum(decode("student_sex",'2',1)) girl_sum from "t_student";

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--6.分数段区间人数

select

case when "score_score" <= 10 then '[0,10]'

when "score_score" > 10 and "score_score" <= 20 then '(10,20]'

when "score_score" > 20 and "score_score" <= 30 then '(20,30]'

when "score_score" > 30 and "score_score" <= 40 then '(30,40]'

when "score_score" > 40 and "score_score" <= 50 then '(40,50]'

when "score_score" > 50 and "score_score" <= 60 then '(50,60]'

when "score_score" > 60 and "score_score" <= 70 then '(60,70]'

when "score_score" > 70 and "score_score" <= 80 then '(70,80]'

when "score_score" > 80 and "score_score" <= 90 then '(80,90]'

when "score_score" > 90 and "score_score" <= 100 then '(90,100]'

end "score",

count(*) "num"

from "t_score"

group by