Oracle Study之---Oracle IN和NOT IN的使用

NOT IN 與 ?IN 的區別:

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not In 相當于<> all,如果 Not In 后面跟的是子查詢的話，子查詢中只要包含一個 null 的返回值，則會造成

整個 Not in 字句返回空值，結果就是查詢不會返回任何結果。

而 in 相當于=any的意思,可以有效處理子查詢中返回空值的情況,返回正確的結果。

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NOT IN示例：

--該例子想要返回沒有下屬的職員的姓名，如果子查詢中有空值返回的話，則整個查詢將沒有結果返回11:20:02?SYS@?test3?>conn?scott/tiger

Connected.

11:21:18?SCOTT@?test3?>select?*?from?emp;

EMPNO?ENAME??????JOB??????????????MGR?HIREDATE???????????????????SAL???????COMM?????DEPTNO

----------?----------?---------?----------?-------------------?----------?----------?----------

7369?SMITH??????CLERK???????????7902?1980-12-17?00:00:00????????800????????????????????20

7499?ALLEN??????SALESMAN????????7698?1981-02-20?00:00:00???????1600????????300?????????30

7521?WARD???????SALESMAN????????7698?1981-02-22?00:00:00???????1250????????500?????????30

7566?JONES??????MANAGER?????????7839?1981-04-02?00:00:00???????2975????????????????????20

7654?MARTIN?????SALESMAN????????7698?1981-09-28?00:00:00???????1250???????1400?????????30

7698?BLAKE??????MANAGER?????????7839?1981-05-01?00:00:00???????2850????????????????????30

7782?CLARK??????MANAGER?????????7839?1981-06-09?00:00:00???????2450????????????????????10

7788?SCOTT??????ANALYST?????????7566?1987-04-19?00:00:00???????3000????????????????????20

7839?KING???????PRESIDENT????????????1981-11-17?00:00:00???????5000????????????????????10

7844?TURNER?????SALESMAN????????7698?1981-09-08?00:00:00???????1500??????????0?????????30

7876?ADAMS??????CLERK???????????7788?1987-05-23?00:00:00???????1100????????????????????20

7900?JAMES??????CLERK???????????7698?1981-12-03?00:00:00????????950????????????????????30

7902?FORD???????ANALYST?????????7566?1981-12-03?00:00:00???????3000????????????????????20

7934?MILLER?????CLERK???????????7782?1982-01-23?00:00:00???????1300????????????????????10

14?rows?selected.

11:20:11?SCOTT@?test3?>select?empno?from?emp

11:20:21???2????????????where?empno?NOT?IN?(select?mgr?from?emp);

no?rows?selected

說明：

Null Values in a Subquery

The SQL statement in the slide attempts to display all the employees who do not have any

subordinates. Logically, this SQL statement should have returned 12 rows. However, the SQL

statement does not return any rows. One of the values returned by the inner query is a null value and,

therefore, the entire query returns no rows

The reason is that all conditions that compare a null value result in a null. So whenever null values

are likely to be part of the resultsset of a subquery, do not use the NOT INoperator. The NOT IN

operator is equivalent to <> ALL.

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IN的示例：

Notice that the null value as part of the results set of a subquery is not a problem if you use the IN

operator. The IN operator is equivalent to =ANY. For example, to display the employees who have

subordinates(下屬), use the following SQL statement:11:20:42?SCOTT@?test3?>select?empno?from?emp

11:21:04???2??????where?empno?in??(select?mgr?from?emp);

EMPNO

----------

7566

7698

7782

7788

7839

7902

6?rows?selected.

---------------------------------------------------------------------------------------------------------Alternatively, a WHERE clause can be included in the subquery to display all employees who do nothave any subordinates:--使用 Not In 的話，要注意除掉子查詢中將要返回的空值11:27:01?SCOTT@?test3?>select?empno?from?emp

11:27:12???2??where?empno?NOT?IN?(select?mgr?from?emp?WHERE?MGR?IS?NOT?NULL);

EMPNO

----------

7844

7521

7654

7499

7934

7369

7876

7900

8?rows?selected.

總結

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