sql - SQL UPDATE SET = 子查询集（随机）

Question

我需要以下（这是伪代码）：

UPDATE Cars SET Engine = (SELECT EngineName FROM Engines WHERE Type = 3)[RANDOMIZE_INDEX_FROM_1_TO_SUBQUERY_COUNT]

所以我基本上需要使用子查询update中Cars table的随机引擎。这可能吗？MSSQL

Answer 1

您可以使用公用表表达式为引擎查询行号，然后选择一个随机行号。

假设您有 100 个引擎 - 查询将如下所示：

;with CTE as (
   SELECT EngineName, ROW_NUMBER() over(order by EngineName) as rn
   FROM Engines WHERE Type = 3
)
UPDATE Cars SET Engine = (SELECT EngineName FROM CTE WHERE where rn = 1+CAST(rand()*100 as int))

更新：对于任何数量的引擎

;with CTE as (
   SELECT EngineName, ROW_NUMBER() over(order by EngineName) as rn
   FROM Engines WHERE Type = 3
)
UPDATE Cars SET Engine = (SELECT EngineName FROM CTE WHERE where rn = 1+CAST(rand()*(SELECT COUNT(1) FROM CTE) as int))

更新 2：多行更新（假设 Cars 表有 ID 字段或您可以排序的任何其他字段）

;WITH CTE_CARS AS (SELECT ENGINE, ROW_NUMBER() OVER (ORDER BY ID) AS RN FROM CARS)
,CTE_ENGINES AS (SELECT EngineName, ROW_NUMBER() OVER (ORDER BY NEWID()) AS RN FROM Engines WHERE Type = 3)
UPDATE CTE_CARS SET CTE_CARS.ENGINE = CTE_ENGINES.EngineName
FROM CTE_CARS JOIN CTE_ENGINES ON CTE_CARS.RN = CTE_ENGINES.RN

更新 3：对于 Cars 多于 enginges 的情况，将最后一个 FROM 替换为

FROM CTE_CARS JOIN CTE_ENGINES ON (CTE_CARS.RN - CTE_ENGINES.RN) % (SELECT COUNT(1) FROM CTE_ENGINES) = 0