第十三天

DML

insert:

SQL> create table t1(x int, y char(1), z date);

SQL> insert into t1(x, y, z) values (99, 'a', sysdate) , (55, '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;

 

子查询：

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;

练习：

在new_dept表中删除没有员工的部门

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

语句类型                   dml                                        ddl

undo数据                  产生大量undo数据       不产生undo数据

空间管理不释放                                 释放

语法                            where                                   删除全部数据

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;

数值：

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);

日期时间：

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;

修改表结构：

SQL> alter table t1 add(e char(10));

SQL> alter table t1 drop(e);

SQL> alter table t1 modify(d not null);

 

约束条件：

字段（列）：not null, check(salary>0)

行与行：primary key, unique

表与表之间：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', 'abc@123.com', 10000, 10);

insert into emp values (100, 'abc', 'abc@123.com', 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', 'def@123.com', 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视图触发器

 

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);           反复执行

SQL> select * from t1;

 

索引：

主键和唯一性约束自动创建索引：

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;                  全表扫描

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