Question

只想问哪个需要更多时间。

以下示例方案：

SELECT *
FROM 
    (SELECT * 
     FROM t1 
     WHERE [Date] BETWEEN "20151012" AND "20151018" 

     UNION ALL 

     SELECT * 
     FROM t2 
     WHERE [Date] BETWEEN "20151012" AND "20151018"

     UNION ALL

     SELECT * 
     FROM t3 
     WHERE [Date] BETWEEN "20151012" AND "20151018" 
) AS T

或本声明：

SELECT * 
FROM 
    (SELECT * FROM t1 

     UNION ALL 

     SELECT * FROM t2 

     UNION ALL

     SELECT * FROM t3) AS T
WHERE 
    [Date] BETWEEN "20151012" AND "20151018"

非常感谢！

Answer 1

我认为最安全，最明确的版本是：

SELECT * 
FROM t1 
WHERE [Date] BETWEEN "20151012" AND "20151018" 

UNION ALL 

SELECT * 
FROM t2 
WHERE [Date] BETWEEN "20151012" AND "20151018"

UNION ALL

SELECT * 
FROM t3 
WHERE [Date] BETWEEN "20151012" AND "20151018"

没有必要希望查询计划能够确定哪些索引可以在子查询中使用。你可能会获得同等的表现，但你不会因为这个而变得更糟。

Answer 2

SQL Server在将谓词推送到基表时没有问题。

您可以检查执行计划以验证这一点。

我更关心字符串文字的双引号。您应该使用单引号，以便查询在默认quoted_identifier设置下正常工作，并且它不会将20151012解释为尝试的列引用。

查询时间执行

2 个答案: