SELECT 문을 사용하여 변수 할당

Question

이상한 행동을 설명해 주시겠습니까?

DECLARE @t VARCHAR(256) = '' 

SELECT @t = @t + CAST(smb.symbol AS VARCHAR(256)) 
FROM (
    SELECT 1,'7' 
    UNION ALL 
    SELECT 2,'8' 
    UNION all 
    SELECT 3,'9' 
) AS smb(n, symbol) 
ORDER BY n 

SELECT @t 

출력 : 나를 위해

789

그게 전부 확인을 클릭합니다.

DECLARE @t VARCHAR(256) = '' 

SELECT @t = @t + CAST(smb.symbol AS VARCHAR(256)) 
FROM (
    SELECT NUMS.N-1 AS N, CHAR(N-1) AS symbol 
    FROM (
     SELECT 1 + n.n1 + nn.n2 * 10 + nnn.n3 * 100 as N 
     FROM (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS n(n1) 
      CROSS JOIN (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS nn(n2) 
      CROSS JOIN (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS nnn(n3) 
    ) AS NUMS 
    WHERE NUMS.N BETWEEN 56 AND 58 
) AS smb(N, symbol) 
ORDER BY smb.N 

SELECT @t 

출력 :

9

그렇다면 번째 예는 마지막 심볼 출력 하는가?

Answer 1

mutlirows 변수 할당을 사용할 때 순서에 의존하지 마십시오.

는 예를 들어이 시도 :

DECLARE @c INT = 0 

SELECT 
@c = @c + x 
FROM (VALUES(1),(2),(3)) AS src(x) 
WHERE x BETWEEN 1 AND 3 
ORDER BY 1 - x DESC 

SELECT @c 

SET @c = 0 

SELECT 
@c = @c + x 
FROM (VALUES(1),(2),(3)) AS src(x) 
WHERE x BETWEEN 1 AND 3 
ORDER BY x DESC 

SELECT @c 

http://sqlmag.com/sql-server/multi-row-variable-assignment-and-order