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《SQL查询语句4》
集合操作
去除重复值：union
不去除重复值：union all
上下两个查询语句中，列的数量和类型要一致，不够可以用空值或设置默认值做替代
select employee_id, job_id from employees
union all
select employee_id, job_id from job_history;
例2：
select employee_id, job_id from employees
union
select employee_id, job_id from job_history;
查询交集：intersect
select employee_id, job_id from employees
intersect
select employee_id, job_id from job_history;
查询差集：minus
select employee_id from employees
minus
select employee_id from job_history;
上下两个查询语句中，列的数量和类型要一致，不够可以用空值或设置默认值做替代
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： //排序语句只能写在最后, 按照表1里面的列进行排序
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（包括增删改查 select insert update delete）
insert:定义列名，values:赋值
SQL> create table t1(x int, y char(1), z date);
SQL> insert into t1(x, y, z) values (1, ‘a‘, sysdate); // 标准写法
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);//对于空值的列，可以省略此列
SQL> insert into t1 values (1, null, sysdate);
将员工表里的内容写到表my_emp中
SQL> create table my_emp as select * from employees; //子查询
SQL> create table my_emp as select last_name, salary from employees where department_id=50; invalid identifier
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:更新（修改） 列
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:删除
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：
Dml（包括增删改查）：不自动提交
ddl：一回车，就直接自动提交，还会把前面的dml也进行提交
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（create alter drop）
Char:定长
Vachar:可变长度
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; b
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
《SQL查询语句4》