oracle连接查询详解

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 MourgosRaphaely works for KingRogers works for KauflingRussell 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)----------        15SCOTT@orcl> select count(1) from dept;  COUNT(1)----------         4SCOTT@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.

select e.employee_id, e.last_name,                e.department_id, d.department_id,                  d.location_idFROM   employees e JOIN departments d ON  e.department_id = d.department_id;

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             1002-APR-01 bottle03-APR-01 bottle04-APR-01 bottle05-APR-01 bottle06-APR-01 bottle             1006-APR-01 bottle              801-APR-01 can                1001-APR-01 can                1502-APR-01 can03-APR-01 can04-APR-01 can                1004-APR-01 can                1105-APR-01 can06-APR-01 can15 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             1002-APR-01 bottle             1003-APR-01 bottle             1004-APR-01 bottle             1005-APR-01 bottle             1006-APR-01 bottle              806-APR-01 bottle              801-APR-01 can                1501-APR-01 can                1502-APR-01 can                1503-APR-01 can                1504-APR-01 can                1104-APR-01 can                1105-APR-01 can                1106-APR-01 can                1115 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;

 

 

 

 

 

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Present by dylan.