Question

select *, (T3.price_usd - T1.price_usd)/T3.price_usd as b
from ticker T1
INNER JOIN mycoins T2
   ON T1.symbol = T2.symbol
INNER JOIN ticker T3
  ON T1.symbol = T3.symbol
WHERE T1.timer = (Select max(timer) from ticker)  
  AND T3.timer = (Select min(timer) from ticker where timer 
                      > (Select max(timer) from ticker - 60*60*24*7*2))

上述代码存在(Select max(timer) from ticker)在查询中多次执行的问题。这是因为多次使用最大计时器值。有没有办法改进这个代码，所以我们可以确定一次最大计时器，然后重新使用该值？

Answer 1

使用以下方法优化您的方案的查询，SQL Server !!

-- Declare Varaibles 
declare @MaxTime int
declare @MinTime int

-- Set values ,Need not to use inside query as recurrncy reduce processing
Select @MaxTime=max(timer) from ticker
Select @MinTime=min(timer) from ticker where timer > (Select max(timer) from ticker - 60*60*24*7*2))


-- Create complex query 
select *, (T3.price_usd - T1.price_usd)/T3.price_usd as b
from ticker T1
INNER JOIN mycoins T2
ON T1.symbol = T2.symbol
INNER JOIN ticker T3
ON T1.symbol = T3.symbol
WHERE T1.timer = @MaxTime  AND
T3.timer = @MinTime

Answer 2

我认为您应该使用存储过程，使用它很容易调整并且对性能有益。

以下是MS SQL Server的示例

CREATE PROCEDURE test
AS
BEGIN
    Declare @max int

    Set @max = (Select max(timer) from ticker);

    select *, (T3.price_usd - T1.price_usd)/T3.price_usd as b
        from ticker T1
        INNER JOIN mycoins T2
        ON T1.symbol = T2.symbol
        INNER JOIN ticker T3
        ON T1.symbol = T3.symbol
        WHERE T1.timer = @max  AND
        T3.timer = (Select min(timer) from ticker where timer > (@max - 60*60*24*7*2))

END
GO

Answer 3

您可以使用：

declare @MaxTime bigint
declare @MinTime bigint

Select @MaxTime = max(timer) from ticker
Select @MinTime = min(timer) from ticker where timer > (@MaxTime - 60*60*24*7*2)

select *, (T3.price_usd - T1.price_usd)/T3.price_usd as b
from ticker T1
INNER JOIN mycoins T2
   ON T1.symbol = T2.symbol
INNER JOIN ticker T3
  ON T1.symbol = T3.symbol
WHERE T1.timer = @MaxTime  
  AND T3.timer = @MinTime

优化SQL以重复计算

3 个答案: