[Database] Read Phenomena in Transaction

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-- Title : [Database] Read Phenomena in Transaction
-- Reference : en.wikipedia.org
-- Key word : dirtyread non-repeatable phantom 더티 읽기 무반복 읽기 팬텀 읽기
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※ Isolation Level Reference : dbrang.tistory.com/848

-- Dirty Read
A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction and not yet committed. 
(다른 트랜잭션이 아직 커밋되지 않은 데이터를 읽을 수 있다.) 

-- Non-Repeatable Read
A non-repeatable read occurs, when during the course of a transaction, a row is retrieved twice and the values within the row differ between reads. 
(데이터를 읽은 후 다른 트랜잭션이 값을 바꾼 다음 다시 읽을 때 데이터가 변경되어 있다.) 

-- Phantom Read
A phantom read occurs when, in the course of a transaction, two identical queries are executed, and the collection of rows returned by the second query is different from the first. 
(데이터를 읽은 후 다른 트랜잭션에서 데이터를 추가했을 때 다시 읽으면 없던 데이터가 포함된다.) 

-- Lost Update
A Lost Update occurs when 2 transactions are update one data and last updated transaction becomes rollback, first committed data is disappeared.