MySQL的PHP​​线性插值表 [英] MySQL php Linear Interpolation of Table

问题描述

我有一个标题为"psytable_moist_air"的表，如下所示:

I have a table titled "psytable_moist_air" shown below:

我正在尝试开发一个MySQL语句，该语句将插入可能在记录之间的值. (如果可以更轻松地用PHP进行数学运算，我也欢迎该解决方案！]

I'm trying to develop a MySQL statement that will interpolate a value that may be between records. ( If it is easier to do the math in PHP I'm open for that solution too!]

示例:我想知道其中"T" = 17.8的"hda"值.

Example: I would like to know the "hda" value where "T" = 17.8.

请注意，没有记录，其中"T" = 17.8.但是，由于该表是线性相关的，因此我可以获得"T" = 17的"hda"值和"T" = 18的"hda"值，并对这些值进行线性插值.

Notice there is no record where "T"=17.8. However, because this table is linearly related, I can get the "hda" value where "T"=17 and the "hda" value where "T"=18 and do a linear interpolation of the values.

结果数学将如下所示:
(获取"hda"值，其中T = 17:hda = 17.102)
(获取"hda"值，其中T = 18:hda = 18.108)

The result math would look like this:
(Get the "hda" value where T=17 : hda = 17.102)
(Get the "hda" value where T=18 : hda = 18.108)

编辑: 我能想到的唯一方法是执行两个MySQL语句以获取越来越小的值:

EDIT: The only way I can think of is to do two MySQL statements to grab the smaller and larger values:

SELECT MAX(`T`), MAX(`hda`) FROM `psytable_moist_air` WHERE `T`<17.8
SELECT MIN(`T`), MIN(`hda`) FROM `psytable_moist_air` WHERE `T`>17.8

然后，我将使用这两个值进行插值.这行得通，但似乎效率很低.谁能提出更好的解决方案?

Then I would use these two values to do the interpolation. This works but seems pretty inefficient. Can anyone come up with a better solution??

如果有人有任何建议，将不胜感激！

If anyone has any advice it would be much appreciated!

.

推荐答案

我认为最好的方法是使用floor函数.

I believe the best way to do this would be to use the floor function.

请参阅以下内容；

SET @x = 17.8;
SET @x0 = FLOOR(@x);
SET @x1 = FLOOR(@x) + 1;

SET @y0 = (SELECT `hda` FROM `psytable_moist_air` WHERE `T` = @x0);
SET @y1 = (SELECT `hda` FROM `psytable_moist_air` WHERE `T` = @x1);

SET @y = @y0 + (@y1 - @y0) * ((@x - @x0) / (@x1 - @x0));

Select @y ,@x0 ,@x1, @y0 ,@y1;

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