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选择一个间隔的几个平均值(select several averages of an interval)

 所以我的同事正在查看一个可以描述为这样的模式：  
+--------------------+-----------+
| DATETIME timestamp | INT value |
+--------------------+-----------+
 
 每隔5分钟输入一行，该值为该时刻的值。  
 这是它变得棘手的地方。 他希望在7天的间隔内获得每8小时的平均值。  
 当然，我可以想到涉及一些客户端代码的解决方案，我们想知道是否有可能在SQL中做更多。  
 所以从本质上说，他想：  
SELECT timestamp, value
  FROM table
 WHERE timestamp >= NOW() - INTERVAL 7 DAYS 
   AND timestamp <= NOW();
 
 然后将其分解为8小时块，并平均每个块的内容。 （每个块应该有12行，每天应该有3个块）。 

So my coworker is looking at a schema which could be described as something like this: 
+--------------------+-----------+
| DATETIME timestamp | INT value |
+--------------------+-----------+
 
Every 5 minutes a row is entered with the value for that moment. 
Here's where it gets tricky. He wants to get the average of every 8 hour period within a 7 day interval. 
Certainly, I can think of solutions which involve some client side code, we were wondering if it was possible to do more in SQL. 
So in essence, he wants: 
SELECT timestamp, value
  FROM table
 WHERE timestamp >= NOW() - INTERVAL 7 DAYS 
   AND timestamp <= NOW();
 
And then breaking that up into 8 hour blocks, and averaging the contents of each block. (each block should have 12 rows, and there should be 3 blocks per day).

原文：https://stackoverflow.com/questions/11743029

更新时间：2023-07-28 08:07

最满意答案

 精确的条件在[[Construct]]内部属性中描述，由new运算符使用：  
 从ECMA-262第三。 版本规格：  
 
  13.2.2 [[Construct]]  
  当调用Function对象F的[[Construct]]属性时，将执行以下步骤：  
  
   创建一个新的本地ECMAScript对象。  
   将Result(1)的[[Class]]属性设置为"Object" 。  
   获取F的原型属性的值。  
   如果Result(3)是一个对象，将Result(1)的[[Prototype]]属性设置为Result(3) 。  
   如果Result(3)不是一个对象，则将Result(1)的[[Prototype]]属性设置为原始Object原型对象，如15.2.3.1所述 。  
   调用F的[[Call]]属性，提供Result(1)作为this值，并将传递给[[Construct]]的参数列表作为参数值。  
   如果Type (Result(6))为Object则返回Result(6) 。  
   退货Result(1) 。  
  
  查看步骤7和8，只有当Result(6)类型Result(6)从F构造函数返回的值） 不是 Object时，才会返回新对象。  

The exact condition is described on the [[Construct]] internal property, which is used by the new operator: 
From the ECMA-262 3rd. Edition Specification: 
 
 13.2.2 [[Construct]] 
 When the [[Construct]] property for a Function object F is called, the following steps are taken: 
  
  Create a new native ECMAScript object. 
  Set the [[Class]] property of Result(1) to "Object". 
  Get the value of the prototype property of F. 
  If Result(3) is an object, set the [[Prototype]] property of Result(1) to Result(3). 
  If Result(3) is not an object, set the [[Prototype]] property of Result(1) to the original Object prototype object as described in 15.2.3.1. 
  Invoke the [[Call]] property of F, providing Result(1) as the this value and providing the argument list passed into [[Construct]] as the argument values. 
  If Type(Result(6)) is Object then return Result(6). 
  Return Result(1). 
  
 Look at steps 7 and 8, the new object will be returned only if the type of Result(6) (the value returned from the F constructor function) is not an Object.

选择一个间隔的几个平均值(select several averages of an interval)

最满意答案

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