源码-Oracle数据库管理-第七章-视图-Part 2

内联视图（Inline View）：一种临时视图，不会存储到数据字典中；当一个Select语句的From子句中又使用了另一个Select语句时，可以说这个查询使用了内联视图。

PS：视图用的还不够熟练，需要多多练习和学习。

--代码 7.11 内联视图使用最简单的例子
SELECT d.deptno, d.dname, emp_cnt.tot
FROM dept d,
(SELECT deptno, COUNT(*) tot
FROM emp
GROUP BY deptno) emp_cnt
WHERE d.deptno = emp_cnt.deptno;

--代码 7.12 使用内联视图获取部门最高薪资级别
SELECT dept.deptno, dept.dname, NVL (MAX (emp_grade.grade), 0)
FROM dept,
(SELECT emp.ename, emp.job, emp.deptno,
(SELECT grade
FROM salgrade
WHERE emp.sal BETWEEN salgrade.losal AND salgrade.hisal) grade
FROM emp) emp_grade
WHERE dept.deptno = emp_grade.deptno(+)
GROUP BY dept.deptno, dept.dname
ORDER BY NVL (MAX (emp_grade.grade), 0) DESC;

/*
Grade/LOSAL/HISAL
1 700 1200
2 1201 1400
3 1401 2000
4 2001 3000
5 3001 9999
*/
select * from salgrade;

--代码 7.13 内联视图的执行示意图
SELECT d.deptno, d.dname, emp_cnt.tot --顶层查询
FROM dept d,
(SELECT deptno, COUNT(*) tot --外层内联查询
FROM
(SELECT * FROM emp WHERE comm IS NOT NULL) --最内层内联查询
GROUP BY deptno) emp_cnt
WHERE d.deptno = emp_cnt.deptno;

--代码7.14 内联视图聚合运算（这部分没搞懂是怎么回事）
SELECT dept.dname, emp_up.empno, emp_up.ename, emp_up.job, dept_avg.avg_sal
FROM (SELECT empno, ename, job, deptno
FROM emp
START WITH empno = 7369
CONNECT BY empno = PRIOR mgr) emp_up,
(SELECT emp.deptno, AVG(emp.sal) avg_sal
FROM emp
GROUP BY deptno) dept_avg,
dept
WHERE emp_up.deptno = dept_avg.deptno AND emp_up.deptno = dept.deptno;

--reference
with x as
( select 'aa' chr from dual
union all
select 'bb' chr from dual)
select level ,chr,lpad( ' ' ,( level - 1 )* 5 , '-' )||chr other from x connect by level <= 3
order by chr;

--不使用内联视图时的SQL语句
UPDATE emp o
SET o.comm = o.sal * 0.2
WHERE o.comm IS NULL AND o.deptno IN (SELECT deptno
FROM (SELECT deptno, COUNT (*) tot
FROM (SELECT *
FROM emp
WHERE comm IS NULL)
GROUP BY deptno)
WHERE tot >= 2);

rollback;

--代码7.15 使用内联视图时的UPDATE语句
UPDATE (SELECT o.comm,o.sal
FROM emp o
WHERE o.comm IS NULL
AND o.deptno IN (SELECT deptno
FROM (SELECT deptno, COUNT (*) tot
FROM (SELECT *
FROM emp
WHERE comm IS NULL)
GROUP BY deptno)
WHERE tot >= 2)) empcomm
SET empcomm.comm = empcomm.sal * 0.2;

rollback;

--使用内联视图进行删除
DELETE FROM (SELECT o.comm,o.sal
FROM emp o
WHERE o.comm IS NULL
AND o.deptno IN (SELECT deptno
FROM (SELECT deptno, COUNT (*) tot
FROM (SELECT *
FROM emp
WHERE comm IS NULL)
GROUP BY deptno)
WHERE tot > 1)) empcomm

--使用Oracle Hint避免ORA-01779异常 (没搞懂！)
UPDATE (SELECT /*+BYPASS_UJVC*/ --使用Oracle提示跳过键检查
a.col2 col2a, b.col2 col2b
FROM test1 a, test2 b
WHERE a.col1 = b.col1)
SET col2a = col2b;