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子查詢

select ename from emp_ning where salary = (select max(salary) from emp_ning);

--誰(shuí)的薪水比tom高?

select ename from emp_ning

where salary > (select salary from emp_ning where ename = 'tom');

insert into emp_ning(empno, ename, salary) values(1020, 'tom', 5000);

--再執(zhí)行

--出錯(cuò):ORA-01427: 單行子查詢,返回了多于一行記錄.

--改進(jìn):

select ename from emp_ning where salary > (select salary from emp_ning where ename = 'tom' and deptno = 10);

--子查詢結(jié)果多于一條記錄,

3000

5000

--比兩條記錄都大: all

--比任何一條大都行: any

select ename ,salary from emp_ning where salary > all (select salary  from emp_ning where ename = 'tom');

--誰(shuí)和tom同部門(mén)?

select ename, deptno from emp_ning where deptno in (select deptno from emp_ning where ename = 'tom')

and ename <> 'tom';

--誰(shuí)的薪水最高?

select ename from emp_ning where salary = (select max(salary) from emp_ning);

--每個(gè)部門(mén)薪水最高的是誰(shuí)?

select ename, salary, deptno from emp_ning

where (deptno, salary)  in( select deptno, max(salary) from emp_ning group by deptno);

--把部門(mén)10和20的兩個(gè)tom薪水都改成10000

update emp_ning

set salary = 10000

where ename = 'tom';

--再查, 查看結(jié)果

數(shù)據(jù)結(jié)構(gòu) 線性表, 樹(shù), 圖

范式 1NF  2NF  3NF