T-SQL NOT IN 有效，但 NOT EXISTS 不

Question

随着新记录添加到 table，我需要将 'level' 的旧记录标记为旧记录。我可以使用 NOT IN 来做到这一点，但 NOT EXISTS 不起作用。我怀疑它与子查询相关性有关，如下所述： NOT EXISTS query doesn't work on Informix while same query with NOT IN works 但我不明白为什么 & 可以使用进一步的解释。下面是一些示例代码：

CREATE TABLE t2 (id INT, level INT, someDate datetime, mostRecent int)
GO
INSERT INTO t2
SELECT 1, 1, '1/1/2010', 1 UNION ALL
SELECT 2, 1, '2/2/2010', 1 UNION ALL
SELECT 3, 2, '3/3/2010', 1 UNION ALL
SELECT 4, 3, '4/4/2010', 1 UNION ALL
SELECT 5, 3, '5/5/2010', 1 UNION ALL
SELECT 6, 3, '6/6/2010', 1 UNION ALL
SELECT 7, 4, '7/7/2010', 1 UNION ALL
SELECT 8, 5, '8/8/2010', 1 UNION ALL
SELECT 9, 6, '9/9/2010', 1 UNION ALL
SELECT 10, 6, '10/10/2010', 1 UNION ALL
SELECT 11, 8, '11/11/2012', 1
GO
-- this doesn't work
UPDATE t2 SET mostRecent = 0
FROM t2
WHERE NOT EXISTS
    (SELECT * FROM t2
    JOIN
        (SELECT level, max(someDate) as someDate FROM t2 group by level) as maxrows
    ON t2.someDate = maxrows.someDate)
GO
-- this works
UPDATE t2 SET mostRecent = 0
FROM t2
WHERE id NOT IN
    (SELECT t2.id FROM t2
    JOIN
        (SELECT level, max(someDate) as someDate FROM t2 group by level) as maxrows
    ON t2.someDate = maxrows.someDate)

Answer 1

你的查询有误，应该是：

UPDATE T SET mostRecent = 0
FROM t2 as T
WHERE NOT EXISTS
    (SELECT * FROM 
     (SELECT level, max(someDate) as someDate FROM t2 group by level) as maxrows
      WHERE T.someDate = maxrows.someDate)

我在 table 中添加了别名以保持清晰

在您的原始查询中，您没有将 NOT EXISTS 查询中的任何内容链接到您的 UPDATE 语句，因此它总是 return 结果，并且它将 "exist" 对于 table 中的每条记录进行更新。

Answer 2

您可以将整个查询重写为这样以获得更好的性能，Joao 的脚本应该已经修复了您描述的错误：

;WITH CTE as
(
  SELECT
    mostrecent, 
    row_number() over (partition by level order by somedate desc) rn
  FROM t2
)
UPDATE CTE
SET 
  mostrecent = 0
WHERE 
  mostrecent = 1
  and rn > 1

T-SQL NOT IN 有效，但 NOT EXISTS 不

T-SQL NOT IN works, but NOT EXISTS does not

sql-server

tsql

not-exists