【转】oracle连接查询详解

转自：http://blog.csdn.net/indexman/article/details/7768811

连接查询是数据库查询语句中使用频率很高的查询方式，下面根据Oracle提供的官方文档学习一下连接查询：

一   Equijoins 等值连接：

     等值连接是条件连接在连接运算符为“=”号时的特例。（相对于非等值连接，如：between...and条件）

    它是从关系R与S的广义笛卡尔积中选取A，B属性值相等的那些元组。

e.g.：

 

SQL> select e.employee_id, e.last_name,
  2                   e.department_id, d.department_id,
  3                   d.location_id
  4  from   employees e, departments d
  5  where  e.department_id = d.department_id;
EMPLOYEE_ID LAST_NAME  DEPARTMENT_ID DEPARTMENT_ID LOCATION_ID
----------- ------------------------- -------------        -------------     -----------
        198              OConnell                              50                           50         1500
        199              Grant                                     50                            50         1500
        200              Whalen                                10                            10          1700
        201              Hartstein                              20                            20         1800
......

 

 

二    Self   joins  自连接：

自连接(self join)是SQL语句中经常要用的连接方式，使用自连接可以将自身表的一个镜像当作另一个表来对待，从而能够得到一些特殊的数据。

e.g.

 

SELECT e1.last_name||' works for '||e2.last_name
   "Employees and Their Managers"
   FROM employees e1, employees e2
   WHERE e1.manager_id = e2.employee_id
      AND e1.last_name LIKE 'R%'
   ORDER BY e1.last_name;

Employees and Their Managers
-------------------------------
Rajs works for Mourgos
Raphaely works for King
Rogers works for Kaufling
Russell works for King

三  Cartesian Products 笛卡尔积：

    If two tables in a join query have no join condition, then Oracle Database returns their Cartesian product.

    如果2个表连接查询而没有连接条件，则oracle返回他们的笛卡尔积。即oracle返回一个表里每一行与另一个表每一行的组合（15 X 4）。

e.g.

 

SCOTT@orcl> select count(1) from emp;

  COUNT(1)
----------
        15
SCOTT@orcl> select count(1) from dept;

  COUNT(1)
----------
         4
SCOTT@orcl> select count(1) from emp, dept;

  COUNT(1)
----------
        60

 

四  Inner Joins  内连接：
     An inner join (sometimes called a simple join) is a join of two or more tables that returns only those rows that satisfy the join condition.
     内连接也叫简单连接，是2个或更多表的关联并且仅返回那些满足连接条件的行。
e.g.

 

<p style="font-weight: bold; font-size: 18px;"></p><pre name="code" class="sql"><span style="font-size:12px;">select e.employee_id, e.last_name,
                e.department_id, d.department_id,
                  d.location_id
FROM   employees e JOIN departments d
 ON  e.department_id = d.department_id;</span></pre><pre name="code" class="html"></pre>

 

 

五   Outer joins 外连接：

  简单连接的扩展。分为左外连接（Left  outer joins）、右外连接（Right  outer joins）、全外连接（Full  outer  joins）

 和Partitioned Outer Joins（分区外连接，用于数据仓库）

Listing 1:

 

SELECT d.department_id, e.last_name

FROM departments d LEFT OUTER JOIN employees e
ON d.department_id = e.department_id
ORDER BY d.department_id, e.last_name;

另外一种写法：

 

SELECT d.department_id, e.last_name
   FROM departments d, employees e
   WHERE d.department_id = e.department_id(+)
   ORDER BY d.department_id, e.last_name;

 

Oracle 官方推荐使用第一种写法。

Listing  2:

 

SELECT d.department_id, e.last_name
   FROM departments d RIGHT OUTER JOIN employees e
   ON d.department_id = e.department_id
   ORDER BY d.department_id, e.last_name;

DEPARTMENT_ID LAST_NAME
------------- -------------------------
. . .
          110 Higgins
          110 Gietz
              Grant
              Zeuss

 

Listing  3: 

 

SELECT d.department_id as d_dept_id, e.department_id as e_dept_id,
      e.last_name
   FROM departments d FULL OUTER JOIN employees e
   ON d.department_id = e.department_id
   ORDER BY d.department_id, e.last_name;

 D_DEPT_ID  E_DEPT_ID LAST_NAME
---------- ---------- -------------------------
  . . .
       110        110 Gietz
       110        110 Higgins
  . . .
       260
       270
                  999 Zeuss
                      Grant

更好的写法，使用USING clause

 

 

SELECT department_id AS d_e_dept_id, e.last_name
   FROM departments d FULL OUTER JOIN employees e
   USING (department_id)
   ORDER BY department_id, e.last_name;

D_E_DEPT_ID LAST_NAME
----------- -------------------------
  . . .
        110 Higgins
        110 Gietz
  . . .
        260
        270
        999 Zeuss
            Grant

 

 

Listing  4:

 

CREATE TABLE inventory (time_id    DATE,
                        product    VARCHAR2(10),
                        quantity   NUMBER);

INSERT INTO inventory VALUES (TO_DATE('01/04/01', 'DD/MM/YY'), 'bottle', 10);
INSERT INTO inventory VALUES (TO_DATE('06/04/01', 'DD/MM/YY'), 'bottle', 10);
INSERT INTO inventory VALUES (TO_DATE('01/04/01', 'DD/MM/YY'), 'can', 10);
INSERT INTO inventory VALUES (TO_DATE('04/04/01', 'DD/MM/YY'), 'can', 10);

SELECT times.time_id, product, quantity FROM inventory
   PARTITION BY  (product)
   RIGHT OUTER JOIN times ON (times.time_id = inventory.time_id)
   WHERE times.time_id BETWEEN TO_DATE('01/04/01', 'DD/MM/YY')
      AND TO_DATE('06/04/01', 'DD/MM/YY')
   ORDER BY  2,1;

TIME_ID   PRODUCT      QUANTITY
--------- ---------- ----------
01-APR-01 bottle             10
02-APR-01 bottle
03-APR-01 bottle
04-APR-01 bottle
05-APR-01 bottle
06-APR-01 bottle             10
06-APR-01 bottle              8
01-APR-01 can                10
01-APR-01 can                15
02-APR-01 can
03-APR-01 can
04-APR-01 can                10
04-APR-01 can                11
05-APR-01 can
06-APR-01 can

15 rows selected.

 

 

更好的写法：

 

SELECT time_id, product, LAST_VALUE(quantity IGNORE NULLS)
   OVER (PARTITION BY product ORDER BY time_id) quantity
   FROM ( SELECT times.time_id, product, quantity
             FROM inventory PARTITION BY  (product)
                RIGHT OUTER JOIN times ON (times.time_id = inventory.time_id)
   WHERE times.time_id BETWEEN TO_DATE('01/04/01', 'DD/MM/YY')
      AND TO_DATE('06/04/01', 'DD/MM/YY'))
   ORDER BY  2,1;

TIME_ID   PRODUCT      QUANTITY
--------- ---------- ----------
01-APR-01 bottle             10
02-APR-01 bottle             10
03-APR-01 bottle             10
04-APR-01 bottle             10
05-APR-01 bottle             10
06-APR-01 bottle              8
06-APR-01 bottle              8
01-APR-01 can                15
01-APR-01 can                15
02-APR-01 can                15
03-APR-01 can                15
04-APR-01 can                11
04-APR-01 can                11
05-APR-01 can                11
06-APR-01 can                11

15 rows selected.

 

 

 六   Anti-joins 反连接：

  返回不满足子查询条件（NOT IN）的左表记录。

e.g.

 

SELECT * FROM employees
   WHERE department_id NOT IN
   (SELECT department_id FROM departments
       WHERE location_id = 1700)
   ORDER BY last_name;

 

  七   Semi-joins 半连接：

   返回匹配exists子查询的左侧没有重复的行。

e.g.

 

SELECT * FROM departments
   WHERE EXISTS
   (SELECT * FROM employees
       WHERE departments.department_id = employees.department_id
       AND employees.salary > 2500)
   ORDER BY department_name;