[ABAP] READ 구문 정리

*Result

SY-SUBRC = 0 “동일하다
SY-SUBRC = 2 “값이 다르다
SY-SUBRC = 4 “해당 조건으로는 인터널테이블 내 데이터가 없다

1. 기본 READ 구문

: 원하는 데이터를 찾고자 할 때 READ 사용.

READ TABLE <ITAB> FROM <WA> (INTO RESULT

[EX]

DATA : GS_STUDENT TYPE ZEDT17_001.
DATA : GS_STUDENT LIKE TABLE OF GS_STUDENT.

DATA : BEGIN OF GS_MAJOR,
	ZCODE  LIKE ZEDT17_001-ZCODE,
	ZPERNR LIKE ZEDT17_001-ZPERNR,
	ZMNAME LIKE ZEDT17_001-ZMNAME,
	END OF GS_MAJOR.
DATA : GT_MAJOR LIKE TABLE OF GS_MAJOR.

CLEAR : GS_STUDENT,GT_STUDENT,GS_MAJOR,GT_MAJOR.

GS_STUDENT-ZPERNR = '00000000001'.
...
APPEND GS_STUDENT TO GT_STUDENT.

GS_MAJOR-ZPERNR = '00000000001'.
GS_MAJOR-MNAME = '경영학과'.
...
APPEND GS_MAJOR TO GT_MAJOR. "각자 다른 인터널테이블에 데이터 입력 

LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	MOVE-CORRESPONDING GS_STUDENT TO GS_MAJOR.
	READ TABLE GT_MAJOR FROM GS_MAJOR INTO GS_MAJOR.

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
						"loop 한번만 돌려도 서로 다른 2개의 인터널테이블의 데이터를 출력 가능
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

---

2. TABLE KEY

READ TABLE <ITAB> WITH TABLE KEY 조건 (INTO RESULT)

[EX]

DATA : GS_STUDENT TYPE ZEDT17_001.
DATA : GS_STUDENT LIKE TABLE OF GS_STUDENT.

DATA : BEGIN OF GS_MAJOR,
	ZCODE  LIKE ZEDT17_001-ZCODE,
	ZPERNR LIKE ZEDT17_001-ZPERNR,
	ZMNAME LIKE ZEDT17_001-ZMNAME,
	END OF GS_MAJOR.
DATA : GT_MAJOR LIKE TABLE OF GS_MAJOR WITH NON-UNIQUE KEY ZCODE.

'' 

LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	READ TABLE GT_MAJOR WITH TABLE KEY ZCODE = GS_STUDENT-ZCODE.
	INTO GS_MAJOR.

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

---

3. WORK AREA 할당

1) 기본

LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	
	READ TABLE GT_MAJOR WITH KEY ZCODE = GS_STUDENT-ZCODE 
															 ZPERNR = GS_STUDENT-ZPERNR
	INTO GS_MAJOR.

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

2) comparing

: READ 구문 수행 결가를 WORK AREA로 할당하는 구문

→ 진짜 있는 데이터인지 확인하는 것

 LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	MOVE-CORRESPONDING GS_STUDENT TO GS_MAJOR.

	READ TABLE GT_MAJOR WITH KEY ZCODE = GS_STUDENT-ZCODE INTO GS_MAJOR
	COMPARING ZCODE.

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

3) transporting

: READ한 결과를 해당 칼럼만 타겟에 저장

 LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	MOVE-CORRESPONDING GS_STUDENT TO GS_MAJOR.

	READ TABLE GT_MAJOR WITH KEY ZCODE = GS_STUDENT-ZCODE INTO GS_MAJOR
	TRANSPORTING ZMNAME.

	IF ST-SUBRC = 0.
		GS_STUDENT-ZKNAME = GS_MAJOR-ZKNAME.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

---

4. INDEX (거의 사용 X)

 LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	MOVE-CORRESPONDING GS_STUDENT TO GS_MAJOR.

	READ TABLE GT_MAJOR INTO GS_MAJOR INDEX SY-TABIX.

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.

---

5. READ BINARY SEARCH

: Read Table 시 데이터를 빠르게 찾아내기 위해 사용

LOOP 안에서 인터널테이블 READ시 FULL SCAN → 성능 저하

이진탐색 알고리즘 기법을 통해 search

*SORT 로 데이터 정렬 후 search

[EX]

SORT GT_STUDENT BY ZCODE.
SORT GT_MAJOR BY ZCODE.

LOOP AT GT_STUDENT INTO GS_STUDENT.
	CLEAR : GS_MAJOR.
	MOVE-CORRESPONDING GS_STUDENT TO GS_MAJOR.

	READ TABLE GT_MAJOR WITH KEY ZCODE = GS_STUDENT-ZCODE INTO GS_MAJOR BINARY SEARCH. 

	IF ST-SUBRC = 0.
		WRITE :/ GS_STUDENT-ZCODE, GS_STUDENT-ZKNAME, GS_MAJOR-ZMNAME.
	ELSE.
		WRITE :/ '데이터를 가져오지 못했습니다'.
	ENDIF.
ENDLOOP.