8月1
DML:select insert update delete(CRUD)
Union和unionall 是重復值的區別 unionall是把所有重復值全保留下來,union是把重復值只保留一個。
Intersect交集。兩個表都有,重復的部分。
Minus集合的差。
集合查詢時,列的數量和數值類型是一樣的。
集合排序時,order by必須寫在最後。
Insert不管怎麽變化,values只代表一行數據。
update更新是說更新列的值
Transactions(交易)的幾個特性:
A原子性
C一致性
I隔離性
D持久性
Ddl不會改變數據庫內部結構。比如:create alter drop
命名必須以字母開頭,列名也必須以字母開頭,數據庫裏合法的字符集都可以作為對象
字符類型:
Char定長
Varchar2 可變長度
約束:
字段:not null(非空) check(檢查約束)
行與行之間:primarykey (PK)主鍵(非空而且唯一) unique 唯一性約束(所有的行在一列上必須是唯一的,可以為空)
表與表之間:
Foreign key(references) 外鍵:確保用戶所寫的編號是真實存在的
集合操作
select employee_id, job_id from employees
union all
select employee_id, job_id from job_history;
select employee_id, job_id from employees
union
select employee_id, job_id from job_history;
select employee_id, job_id from employees
intersect
select employee_id, job_id from job_history;
select employee_id from employees
minus
select employee_id from job_history;
select employee_id, job_id, salary from employees
union all
select employee_id, job_id, null from job_history;
select employee_id, job_id, to_char(salary) from employees
union all
select employee_id, job_id, ‘no salary‘ from job_history;
集合排序:
select employee_id, job_id, salary from employees
union all
select employee_id, job_id, null from job_history
order by salary;
select employee_id, job_id, null from job_history
union all
select employee_id, job_id, salary from employees
order by 3;
DML
insert:
SQL> create table t1(x int, y char(1), z date);
SQL> insert into t1(x, y, z) values (1, ‘a‘, sysdate);
SQL> insert into t1(x, z, y) values (2, sysdate+1, ‘b‘);
SQL> insert into t1(x, y, z) values (1, null, sysdate);
SQL> insert into t1(x, z) values (2, sysdate+1);
SQL> insert into t1 values (1, null, sysdate);
SQL> create table my_emp as select * from employees;
SQL> create table my_emp as select last_name, salary from employees where department_id=50;
SQL> create table avg_sal as select department_id, avg(salary) avg_sal from employees group by department_id;
SQL> create table my_emp as select * from employees where 1=0;
SQL> insert into my_emp select * from employees;
update:
SQL> update my_emp set salary=salary*1.1;
SQL> update my_emp set salary=salary*1.1 where department_id=50;
SQL> update my_emp set salary=salary*1.1, commission_pct=0.5 where employee_id=197;
delete:
SQL> delete from my_emp where employee_id=197;
SQL> delete from my_emp where department_id=50;
SQL> delete from my_emp;
子查詢:
SQL> create table my_emp as select * from employees;
SQL> alter table my_emp add(department_name varchar2(30));
SQL> update my_emp outer set department_name=(select department_name from departments where department_id=outer.department_id);
update (select t1.department_name as aname,t2.department_name bname from my_emp t1 ,departments t2 where t1.department_id=t2.department_id) set aname=bname;
練習:
在new_dept表中刪除沒有員工的部門
SQL> create table my_dept as select * from departments;
delete from my_dept outer
where not exists
(select 1 from my_emp
where department_id=outer.department_id);
delete和truncate:
delete truncate
語句類型 dml ddl
undo數據 產生大量undo數據 不產生undo數據
空間管理 不釋放 釋放
語法 where 刪除全部數據(回車自動生效,不能恢復)
DDL
字符串:
SQL> create table t1(x char(10), y varchar2(10));
SQL> insert into t1 values(‘x‘, ‘y‘);
SQL> select dump(x), dump(y) from t1;
數值:
SQL> create table t1(x number(5,2), y number(5));
SQL> insert into t1 values (123.45, 12345);
SQL> insert into t1 values (12.345, 12345);
SQL> insert into t1 values (12.345, 123.45);
SQL> select * from t1;
SQL> insert into t1 values (12.345, 112345);
日期時間:
SQL> create table t1(a date, b timestamp, c timestamp with time zone, d timestamp with local time zone);
SQL> insert into t1 values (sysdate, systimestamp, systimestamp, systimestamp);
SQL> alter session set time_zone=‘+9:00‘;
SQL> select * from t1;
修改表結構:
SQL> alter table t1 add(e char(10));
SQL> alter table t1 drop(e);
SQL> alter table t1 modify(d not null);
約束條件:
字段(列):not null, check(salary>0)
行與行:primary key, unique
表與表之間:foreign key
create table dept (
deptno int constraint dept_deptno_pk primary key,
dname varchar2(20) constraint dept_dname_nn not null);
create table emp (
empno int constraint emp_empno_pk primary key,
ename varchar2(20) constraint emp_ename_nn not null,
email varchar2(50) constraint emp_email_uq unique,
salary int constraint emp_salary_ck check(salary>0),
deptno int constraint emp_deptno_fk references dept(deptno))
SQL> select constraint_name, constraint_type from user_constraints where table_name in(‘DEPT‘, ‘EMP‘);
SQL> insert into emp values (100, ‘abc‘, [email protected], 10000, 10);
insert into emp values (100, ‘abc‘, [email protected], 10000, 10)
*
ERROR at line 1:
ORA-02291: integrity constraint (HR.EMP_DEPTNO_FK) violated - parent key not
found
SQL> insert into dept values (10, ‘sales‘);
1 row created.
SQL> insert into dept values (10, ‘market‘);
insert into dept values (10, ‘market‘)
*
ERROR at line 1:
ORA-00001: unique constraint (HR.DEPT_DEPTNO_PK) violated
SQL> insert into dept values (20, ‘market‘);
1 row created.
SQL> commit;
Commit complete.
SQL> insert into emp values (101, ‘def‘, [email protected], 10000, 20);
create table emp (
empno int constraint emp_empno_pk primary key,
ename varchar2(20) constraint emp_ename_nn not null,
email varchar2(50) constraint emp_email_uq unique,
salary int constraint emp_salary_ck check(salary>0),
deptno int constraint emp_deptno_fk references dept(deptno) on delete set null)或者on delete cascade
instead of trigger視圖觸發器
序列:
SQL> create sequence test_seq increment by 1 start with 1 maxvalue 1000 nocycle cache 20;
SQL> create table t1(x int primary key, y int);
SQL> insert into t1 values (test_seq.nextval, 11); 反復執行
SQL> select * from t1;
索引:
主鍵和唯一性約束自動創建索引:
SQL> select constraint_name, constraint_type from user_constraints where table_name=‘EMPLOYEES‘;
SQL> select index_name, index_type from user_indexes where table_name=‘EMPLOYEES‘;
SQL> set autot on
SQL> select last_name from employees where employee_id=100; 走索引
SQL> select email from employees; 走索引
SQL> select last_name from employees where salary=2100; 全表掃描
SQL> create index emp_salary_ix on employees(salary);
SQL> select last_name from employees where salary=2100; 走索引
SQL> set autot off
8月1