Microsoft SQL Server
커서

통사론

• DECLARE cursor_name CURSOR [지역 | 글로벌]
  • [FORWARD_ONLY | 스크롤]
    [정적 | 키셋 | 다이나믹 | 빨리 감기 ]
    [READ_ONLY | SCROLL_LOCKS | 최적 [OPTIMISTIC]
    [TYPE_WARNING]
  • FOR select_statement
  • [FOR UPDATE [OF column_name [, ... n]]]

비고

기본 전달 전용 커서

일반적으로 성능에 부정적인 영향을 줄 수 있으므로 커서를 사용하지 않는 것이 좋습니다. 그러나 일부 특수한 경우에는 레코드별로 데이터 레코드를 반복하고 일부 작업을 수행해야 할 수도 있습니다.

DECLARE @orderId AS INT

-- here we are creating our cursor, as a local cursor and only allowing 
-- forward operations
DECLARE rowCursor CURSOR LOCAL FAST_FORWARD FOR
    -- this is the query that we want to loop through record by record
    SELECT [OrderId]
    FROM [dbo].[Orders]

-- first we need to open the cursor
OPEN rowCursor

-- now we will initialize the cursor by pulling the first row of data, in this example the [OrderId] column,
-- and storing the value into a variable called @orderId
FETCH NEXT FROM rowCursor INTO @orderId

-- start our loop and keep going until we have no more records to loop through
WHILE @@FETCH_STATUS = 0 
BEGIN

    PRINT @orderId
    
    -- this is important, as it tells SQL Server to get the next record and store the [OrderId] column value into the @orderId variable
    FETCH NEXT FROM rowCursor INTO @orderId

END

-- this will release any memory used by the cursor
CLOSE rowCursor
DEALLOCATE rowCursor

기본 커서 구문

몇 가지 예제 테스트 행에서 작동하는 간단한 커서 구문 :

/* Prepare test data */
DECLARE @test_table TABLE
(
    Id INT,
    Val VARCHAR(100)
);
INSERT INTO @test_table(Id, Val)
VALUES 
    (1, 'Foo'), 
    (2, 'Bar'), 
    (3, 'Baz');
/* Test data prepared */

/* Iterator variable @myId, for example sake */
DECLARE @myId INT;

/* Cursor to iterate rows and assign values to variables */
DECLARE myCursor CURSOR FOR
    SELECT Id
    FROM @test_table;

/* Start iterating rows */
OPEN myCursor;
FETCH NEXT FROM myCursor INTO @myId;

/* @@FETCH_STATUS global variable will be 1 / true until there are no more rows to fetch */
WHILE @@FETCH_STATUS = 0
BEGIN

    /* Write operations to perform in a loop here. Simple SELECT used for example */
    SELECT Id, Val
    FROM @test_table 
    WHERE Id = @myId;

    /* Set variable(s) to the next value returned from iterator; this is needed otherwise the cursor will loop infinitely. */
    FETCH NEXT FROM myCursor INTO @myId;
END
/* After all is done, clean up */
CLOSE myCursor;
DEALLOCATE myCursor;

SSMS 결과. 이들은 모두 별도의 쿼리이므로 아무 것도 통합되지 않습니다. 쿼리 엔진이 각 반복을 하나의 집합이 아닌 하나씩 처리하는 방법에 유의하십시오.