Select MAX TIMESTAMP 作为 BIGINT 来自 SQL table

Question

我担心以下查询的性能：

SELECT 
    MAX(CAST((CONVERT(bigint, DBTimeStamp)) AS decimal)) AS DBTimeStamp 
FROM Category 
WHERE DepartmentID = 5

是否有更快的方法从 table 获取 biggest/latest 时间戳作为整数？

Answer 1

如果在转换和转换之前计算最大值 SQL 可以使用索引并且只需要转换和转换一次:

SELECT 
CAST(CONVERT(bigint,MAX( DBTimeStamp)) AS decimal) AS DBTimeStamp 
FROM Category 
WHERE DepartmentID = 5

Select MAX TIMESTAMP as BIGINT from SQL table