1. 程式人生 > >8月1

8月1

truncate ger group by nextval cascade mes dml trigge start

DMLselect insert update deleteCRUD

Unionunionall 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 keyreferences) 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:

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);

deletetruncate

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