1. MERGE INTO 구문

MERGE INTO
USING
ON
WHEN MATCHED THEN UPDATE SET
DELETE -- 오직 MATCHED에만 가능. UPDATE된 대상에 대해서(즉, 조인된 대상에 대해서)
WHEN NOT MATCHED THEN 
INSERT (a,b,c) VALUES ( 'a','b','c');

1. 힌트

NO_EXPAND ↔ USE_CONCAT

1. 제약조건

ALTER TABLE TAB ADD CONSTRAINT 
	CONSTRAINT_NAME PRIMARY KEY (a,b) USING INDEX INDEX_NAME;
ALTER TABLE TAB ADD CONSTRAINT
 CONSTRAINT_NAME FOREIGN KEY (c) REFERENCES TAB2(col);
ALTER TABLE TAB MODIFY CONSTRAINT CONSTRAINT_NAME DISABLE DROP INDEX;
ALTER TABLE 테이블명 DROP PRIMARY KEY DROP INDEX;

CREATE TABLE A (
	id number unique,
    col1 varchar2(20),
    **fk_col** number,
	constraint pk_A PRIMARY KEY (id),
	constraint fk_A foreign key (**fk_col**) references B(id)
);

CREATE TABLE A (
	id number unique PRIMARY KEY,
  dd number foreign key references B(id)
);

1. 참조무결성

INSERT

• Automatic
• set null
• set default
• dependent
• no Action

UPDATE,DELETE