常見的SQL命令(2)
創建學生情況表:student
create table student(st_class CHAR(8),st_no CHAR(10) NOT NULL,st_name CHAR(8) NOT NULL,st_sex CHAR(2),st_age SMALLINT,PRIMARY KEY(st_no))
創建課程設置表:subject
create table subject(su_no CHAR(4) NOT NULL,su_subject CHAR(20) NOT NULL,su_credit INTEGER,su_period INTEGER,su_preno CHAR(4),PRIMARY KEY(su_no))
創建學生選課表:score
create table score (st_no CHAR(10),st_nom CHAR(4),st_score INTEGERR NULL,FOREIGN KEY(st_no) REFERENCE student)
查看表結構:DESC student
刪除表: DROP TABLE student,score
添加字段: alter table student add (st_born date not null)
刪除字段: alter table student drop (st_age)
修改字段類型和長度:
alter table student alter column name varchar(23) null
視圖
從student表中導出只包括女學生情況的視圖:
create view womanview as select st_class,st_no,st_name,st_age from student where
st_sex="女"
從student和score表中創建分數在60分以上的女學生視圖:
create view woman_score as select student.st_class student.st_no,student.st_name,
student.st_age,score.sc_score from student score where student.st_sex="女" and
score.sc_score >= 60 and student.st_no=score.st_no
查看 woman_score 視圖
select * from woman_score
索引
對基本表student 中 st_no 和 st_age 創建索引,分別為升序和降序排列
create unique index stindex on student (st_no ASC,st_age DESC)
刪除索引:
drop index stindex
SELECT查詢
JOIN ON 語句 聯接
WHERE 語句 指定查詢條件
ORDER BY 語句 指定排序字段和排序方式
GROUP BY 和 HAVING 語句 分組
DISTINCT 語句和 UNIQUE 語句 指定是否要重復記錄
TOP語句 列在最前
WHERE子句中的操作符和運算函數
算術比較運算符: < <= > >= = <>
邏輯運算符: AND,OR,NOT
集合運算符: UNION(並),INTERSECT(交),EXCEPT(差)
集合成員資格運算符: IN,NOT IN
謂詞: EXISTS(存在) , ALL ,SOME, UNIQUE
聚合函數: AVG,MIN,MAX,SUM,COUNT(計數)
條件查詢:
select unique student.st_class,student.st_no,student.st_name,student.sex,
student.st.age,score.su_no,score.score
排序查詢:
查不及格的課程,並將課程號按從大到小排列
select unique su_no from score where score<60 order by su_no DESC
嵌套查詢:
查詢課程編號為C03,且課程成績在80分以上的學生的學號和姓名
select st_no,st_name from student where st_no in (select st_no from score where su_no = ‘c03‘ and score>80)
計算查詢:
查詢男學生總人數和平均年齡:
select count(*),AVG(st_age) from student where st_sex=‘男‘
統計選修課程人數:
select count(DISTINCT st_no) from score
數據更新
INSERT語句:insert into score(st_no,su_no,score) value (‘10002‘,‘c02‘,95)
DELETE語句:delete from student where st_no = ‘10002‘
UPDATE語句:update subject set su_subject = ‘英語‘ where su_no = ‘c02‘
數據控制
安全性控制、完整性控制、事務控制和並發控制
授權語句:grant connect to sse identified by password
grant resource to sse
grant dba to sse
權力回收:
revoke connect from sse
revoke resource from sse
將表student 查詢權授予所有用戶:
grant select on student to public
將表 subject 的插入及修改權力授予用戶SSE並使得他具有將這種權力授予其他人的權力
grant insert,update(su_subject) on subject to sse with grant option
常見的SQL命令(2)