mysql - 在 MySQL SELECT 查询中，我可以在 WHERE 规范中使用我的 "AS column"吗？

Question

在我的数据库中，我计算节点之间的距离:

SELECT DISTINCT
       dest.name,
       AsText(orig.location),
       AsText(dest.location),
       round((glength(linestringfromwkb(linestring((orig.location), (dest.location)))))) as distance
FROM nodes orig,
     nodes dest
WHERE orig.name='GERP'

我要补充

and distance < dest.visibility

在最后，但我被告知距离是一个未知列。

非常感谢任何见解。

Answer 1

使用子查询，那么你只需要输入一次公式(如果你需要改变它，你只需要改变一次)。

SELECT
       dest.name,
       dest.visibility,
       AsText(orig.location),
       AsText(dest.location),
       distance
FROM (
SELECT DISTINCT
       dest.name,
       dest.visibility,
       AsText(orig.location),
       AsText(dest.location),
       round((glength(linestringfromwkb(linestring((orig.location), (dest.location)))))) as distance
FROM nodes orig,
     nodes dest
WHERE orig.name='GERP'
) AS nodeDistances
WHERE nodeDistainces.distance < visibility