이번에는 자바스크립트의 함수에 대해서 알아보도록 하겠습니다.  

함수가 뭐냐? 모르시는 분이 계시려나요? 자바나 C의 메소드, 함수랑 똑같은 겁니다.

함수는 function 키워드를 이용해서 정의하는데 function의 영어 의미를 찾아보면 다음과 같습니다.

1.명사 (사람사물의) 기능
2.명사 행사, 의식
3.동사 (제대로) 기능하다[작용하다] (=operate)

따라서 함수는 특정 기능을 하는 놈이구나~ 라고  이해하시면 됩니다.

내가 원하는 어떤 기능을 하도록 만드는 것이죠.

자, 그럼 문법을 한번 살펴보겠습니다.

<script type="text/javascript">

function 함수명( 파라미터 리스트 )
{
  // statements
}

</script>

위 문법은 함수를 선언하는 것입니다. 아래처럼 사용할 수 있죠. 

<script type="text/javascript">

function sayHello()
{
   alert("Hello there");
}

</script>

자, 그럼 이렇게 선언해놓은 함수를 어떻게 호출을 할까요?

네~ 그렇죠~ 제가 늘 말하는 "아래처럼" 호출하면 되는겁니다~

<script type="text/javascript">

sayHello();

</script>

파라미터

이번에는 파라미터 사용법에 대해서 알아보도록 하겠습니다.

자바스크립트의 특징 중 하나가  undefined type이었다는 것을 기억하시나요? 변수를 지정할때 타입을 지정하지를 않죠?  

함수내에 파라미터를 넣을때도 타입을 지정하지 않습니다. 아래처럼 말이죠. 

<script type="text/javascript">

function sayHello(name, age)
{
   alert( name + " is " + age + " years old.");
}

</script>

위 소스를 보시면 sayHello()가 파라미터 두개를 받고있네요. name과 age.  

이 함수를 호출할 때에는 파라미터를 두개 넣어주면 되는 겁니다. 

<script type="text/javascript">

sayHello('Zara', 7 );

</script>

sayHello 함수에 'Zara' 랑 7을 파라미터로 넘겼네요. Zara의 홑따옴표는 스트링을 의미합니다. Zara라는 스트링을 파라미터로 넘긴다는 말이죠. 

return문

자바스크립트의 함수도 결과값을 반환할 수 있습니다. 

예제를 한번 볼까요? 

<script type="text/javascript">

function concatenate(first, last)
{
   var full;

   full = first + last;
   return  full;
}

</script>

위 소스는 두개의 파라미터를 받아서 두개를 합친 결과를 반환합니다.

이제 함수를 호출해서 함수에서 얻은 결과값을 경고창에 띄워보겠습니다. 

<script type="text/javascript">

   var result;
   result = concatenate('Zara', 'Ali');
   alert(result );

</script>

함수에 대해서 좀 더 자세한 내용을 알고싶으면 아래 링크를 참조하세요 ^____^

• JavaScript Nested Functions

• JavaScript Function( ) Constructor

• JavaScript Function Literals

Reference : http://www.tutorialspoint.com/javascript/javascript_functions.htm 

자 오늘은 concat()과 listagg()에 대해서 알아보도록 하겠습니다.

DB에서 정보를 추출할 때 여러줄(리스트 형태)로 나오는 것들을 한줄로 합쳐서 뽑아내고 싶거나  

한 줄에 여러 필드들이 있을때 이 필드들을 모두 합쳐서 한줄의 스트링으로 뽑아내고 싶을 때가 있을거에요.

예를들면 EMP테이블에 한명의 employee만 등록이 되어있다고 가정합시다.

이때 이 사람의 정보를 emp_nm 과 emp_id를 나눠서 emp객체의 name과 id필드에 뽑아올 수도 있지만 궂이 이걸 하나의 String으로 뽑아내고 싶을때가 있을 수도 있다고 가정하고 -_-ㅋ

emp_nm | emp_id

---------------

장군이   |     3

이렇게 데이터가 들어있을 때 "3장군이" 라는 스트링을 뽑아오려면 concat을 쓰면 됩니다.

select concat( emp_id, emp_nm) from emp; 

이제 데이타가 한줄 더 들어와서 두명의 employee가 있다고 가정합시다.

emp_nm | emp_id

---------------

장군이   |     3

이쁭이   |     5

그리고 이 직원들의 이름을 쉼표로 구분해서 하나의 스트링으로 뽑아내고 싶다고 가정합시다.

"장군이,이쁭이" 이렇게 말이죠.

이럴때는 listagg()를 쓰면 됩니다. 아래처럼 말이죠.

select listagg(emp_nm, ',') within group ( order by emp_id ) from emp; 

listagg(리스트애그)에 대한 자세한 내용은 아래 출처에 있는 주소로 가시면 좀 더 자세한 설명을 보실 수 있습니다.

그럼 좋은하루 되세요~ ^_^ 

출처 : http://oracle-base.com/articles/misc/string-aggregation-techniques.php ( listagg() )  

링크가 break될 것을 우려하여 밑에 위 링크로가면 볼 수 있는 내용을 가져왔습니다. ^^

--------------------------------------------------------------------------------

String Aggregation Techniques

On occasion it is necessary to aggregate data from a number of rows into a single row, giving a list of data associated with a specific value. Using the SCOTT.EMP table as an example, we might want to retrieve a list of employees for each department. Below is a list of the base data and the type of output we would like to return from an aggregate query.

Base Data:

    DEPTNO ENAME
---------- ----------
        20 SMITH
        30 ALLEN
        30 WARD
        20 JONES
        30 MARTIN
        30 BLAKE
        10 CLARK
        20 SCOTT
        10 KING
        30 TURNER
        20 ADAMS
        30 JAMES
        20 FORD
        10 MILLER

Desired Output:

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,FORD,ADAMS,SCOTT,JONES
        30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD

This article is based on a thread from asktom.oracle.com and contains several methods to achieve the desired results.

• LISTAGG Analytic Function in 11g Release 2
• WM_CONCAT Built-in Function (Not Supported)
• User-Defined Aggregate Function
• Specific Function
• Generic Function using Ref Cursor
• ROW_NUMBER() and SYS_CONNECT_BY_PATH functions in Oracle 9i
• COLLECT function in Oracle 10g

LISTAGG Analystic Function in 11g Release 2

The LISTAGG analytic function was introduced in Oracle 11g Release 2, making it very easy to aggregate strings. The nice thing about this function is it also allows us to order the elements in the concatenated list. If you are using 11g Release 2 you should use this function for string aggregation.

COLUMN employees FORMAT A50

SELECT deptno, LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 ADAMS,FORD,JONES,SCOTT,SMITH
        30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD

3 rows selected.

WM_CONCAT Built-in Function (Not Supported)

If you are not running 11g Release 2, but are running a version of the database where the WM_CONCAT function is present, then it is a zero effort solution as it performs the aggregation for you. It is actually an example of a user defined aggregate function described below, but Oracle have done all the work for you.

COLUMN employees FORMAT A50

SELECT deptno, wm_concat(ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,FORD,ADAMS,SCOTT,JONES
        30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD

3 rows selected.

Note. WM_CONCAT is an undocumented function and as such is not supported by Oracle for user applications (MOS Note ID 1336219.1). If this concerns you, use a User-Defined Aggregate Function described below.

User-Defined Aggregate Function

The WM_CONCAT function described above is an example of a user-defined aggregate function that Oracle have already created for you. If you don't want to use WM_CONCAT, you can create your own user-defined aggregate function as described at asktom.oracle.com.

CREATE OR REPLACE TYPE t_string_agg AS OBJECT
(
  g_string  VARCHAR2(32767),

  STATIC FUNCTION ODCIAggregateInitialize(sctx  IN OUT  t_string_agg)
    RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateIterate(self   IN OUT  t_string_agg,
                                       value  IN      VARCHAR2 )
     RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateTerminate(self         IN   t_string_agg,
                                         returnValue  OUT  VARCHAR2,
                                         flags        IN   NUMBER)
    RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateMerge(self  IN OUT  t_string_agg,
                                     ctx2  IN      t_string_agg)
    RETURN NUMBER
);
/
SHOW ERRORS


CREATE OR REPLACE TYPE BODY t_string_agg IS
  STATIC FUNCTION ODCIAggregateInitialize(sctx  IN OUT  t_string_agg)
    RETURN NUMBER IS
  BEGIN
    sctx := t_string_agg(NULL);
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateIterate(self   IN OUT  t_string_agg,
                                       value  IN      VARCHAR2 )
    RETURN NUMBER IS
  BEGIN
    SELF.g_string := self.g_string || ',' || value;
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateTerminate(self         IN   t_string_agg,
                                         returnValue  OUT  VARCHAR2,
                                         flags        IN   NUMBER)
    RETURN NUMBER IS
  BEGIN
    returnValue := RTRIM(LTRIM(SELF.g_string, ','), ',');
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateMerge(self  IN OUT  t_string_agg,
                                     ctx2  IN      t_string_agg)
    RETURN NUMBER IS
  BEGIN
    SELF.g_string := SELF.g_string || ',' || ctx2.g_string;
    RETURN ODCIConst.Success;
  END;
END;
/
SHOW ERRORS


CREATE OR REPLACE FUNCTION string_agg (p_input VARCHAR2)
RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING t_string_agg;
/
SHOW ERRORS

The aggregate function is implemented using a type and type body, and is used within a query.

COLUMN employees FORMAT A50

SELECT deptno, string_agg(ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,FORD,ADAMS,SCOTT,JONES
        30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD

3 rows selected.

Specific Function

One approach is to write a specific function to solve the problems. The get_employees function listed below returns a list of employees for the specified department.

CREATE OR REPLACE FUNCTION get_employees (p_deptno  in  emp.deptno%TYPE)
  RETURN VARCHAR2
IS
  l_text  VARCHAR2(32767) := NULL;
BEGIN
  FOR cur_rec IN (SELECT ename FROM emp WHERE deptno = p_deptno) LOOP
    l_text := l_text || ',' || cur_rec.ename;
  END LOOP;
  RETURN LTRIM(l_text, ',');
END;
/
SHOW ERRORS

The function can then be incorporated into a query as follows.

COLUMN employees FORMAT A50

SELECT deptno,
       get_employees(deptno) AS employees
FROM   emp
GROUP by deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,JONES,SCOTT,ADAMS,FORD
        30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES

3 rows selected.

To reduce the number of calls to the function, and thereby improve performance, we might want to filter the rows in advance.

COLUMN employees FORMAT A50

SELECT e.deptno,
       get_employees(e.deptno) AS employees
FROM   (SELECT DISTINCT deptno
        FROM   emp) e;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,JONES,SCOTT,ADAMS,FORD
        30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
        
3 rows selected.

Generic Function using Ref Cursor

An alternative approach is to write a function to concatenate values passed using a ref cursor. This is essentially the same as the previous example, except that the cursor is passed in making it generic, as shown below.

CREATE OR REPLACE FUNCTION concatenate_list (p_cursor IN  SYS_REFCURSOR)
  RETURN  VARCHAR2
IS
  l_return  VARCHAR2(32767); 
  l_temp    VARCHAR2(32767);
BEGIN
  LOOP
    FETCH p_cursor
    INTO  l_temp;
    EXIT WHEN p_cursor%NOTFOUND;
    l_return := l_return || ',' || l_temp;
  END LOOP;
  RETURN LTRIM(l_return, ',');
END;
/
SHOW ERRORS

The CURSOR function is used to allow a query to be passed to the function as a ref cursor, as shown below.

COLUMN employees FORMAT A50

SELECT e1.deptno,
       concatenate_list(CURSOR(SELECT e2.ename FROM emp e2 WHERE e2.deptno = e1.deptno)) employees
FROM   emp e1
GROUP BY e1.deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,JONES,SCOTT,ADAMS,FORD
        30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES

3 rows selected.

Once again, the total number of function calls can be reduced by filtering the distinct values, rather than calling the function for each row.

COLUMN employees FORMAT A50

SELECT deptno,
       concatenate_list(CURSOR(SELECT e2.ename FROM emp e2 WHERE e2.deptno = e1.deptno)) employees
FROM   (SELECT DISTINCT deptno
        FROM emp) e1;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,JONES,SCOTT,ADAMS,FORD
        30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES

3 rows selected.

ROW_NUMBER() and SYS_CONNECT_BY_PATH functions in Oracle 9i

An example on williamrobertson.net uses the ROW_NUMBER() and SYS_CONNECT_BY_PATH functions to achieve the same result without the use of PL/SQL or additional type definitions.

SELECT deptno,
       LTRIM(MAX(SYS_CONNECT_BY_PATH(ename,','))
       KEEP (DENSE_RANK LAST ORDER BY curr),',') AS employees
FROM   (SELECT deptno,
               ename,
               ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename) AS curr,
               ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename) -1 AS prev
        FROM   emp)
GROUP BY deptno
CONNECT BY prev = PRIOR curr AND deptno = PRIOR deptno
START WITH curr = 1;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 ADAMS,FORD,JONES,SCOTT,SMITH
        30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD

3 rows selected.

COLLECT function in Oracle 10g

An example on oracle-developer.net uses the COLLECT function in Oracle 10g to get the same result. This method requires a table type and a function to convert the contents of the table type to a string. I've altered his method slightly to bring it in line with this article.

CREATE OR REPLACE TYPE t_varchar2_tab AS TABLE OF VARCHAR2(4000);
/

CREATE OR REPLACE FUNCTION tab_to_string (p_varchar2_tab  IN  t_varchar2_tab,
                                          p_delimiter     IN  VARCHAR2 DEFAULT ',') RETURN VARCHAR2 IS
  l_string     VARCHAR2(32767);
BEGIN
  FOR i IN p_varchar2_tab.FIRST .. p_varchar2_tab.LAST LOOP
    IF i != p_varchar2_tab.FIRST THEN
      l_string := l_string || p_delimiter;
    END IF;
    l_string := l_string || p_varchar2_tab(i);
  END LOOP;
  RETURN l_string;
END tab_to_string;
/

The query below shows the COLLECT function in action.

COLUMN employees FORMAT A50

SELECT deptno,
       tab_to_string(CAST(COLLECT(ename) AS t_varchar2_tab)) AS employees
FROM   emp
GROUP BY deptno;
       
    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,JONES,SCOTT,ADAMS,FORD
        30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
        
3 rows selected.

이상입니다!!!