mysql - MySqlは結果として新しい列を追加します

Question

私はこのクエリを持っています：

SELECT v2.longitude AS something FROM points AS v2

今、私はこのようなことをしたいと思います：

SELECT v2.longitude AS something,2*something FROM points AS v2

しかし、それは失敗します

points.longitude浮動小数点数です

どうすればこれを修正できますか？

編集-これは現在のクエリの例です：

$query="
SELECT 
v2.longitude AS xa,
v2.latitude AS ya,
v3.longitude AS xb,
v3.latitude AS yb, 
(yb-ya)/(xb-xa) AS l,
-1/l AS l_katheto,
(l*xa-l_katheto*$tetmimenh+ya-y1)/(l_katheto-l) AS x_tomh, 
l*(x_tomh-xa)+ya AS y_katheto,
min(
    sqrt(
        (v2.longitude-$tetmimenh)*
        (v2.longitude-$tetmimenh)+
        (v2.latit‌​ude-$tetagmenh)*
        (v2.latitude-$tetagmenh)
    ),
    sqrt(
        (v3.longitude-$tetmimenh)*
        (v3.long‌​itude-$tetmimenh)+
        (v3.latitude-$tetagmenh)*
        (v3.latitude-$tetagmenh)
    ),
    sqrt(
        ($tetmi‌​menh-x_tomh)*
        ($tetmimenh-x_tomh)+
        ($tetagmenh-y_tomh)*
        ($tetagmenh-y_tomh)
    )
) 
FROM 
segments AS v1 
JOIN points AS v2 ON v1.from_point=v2.point_id 
JOIN points AS v3 ON v3.point_id=v1.to_point";

Answer 1

このコードを試してください：

SELECT v2.longitude AS something,2*v2.longitude AS something2 FROM points AS v2

Answer 2

ここで何を達成しようとしているのか正確にはわかりませんが、以前のコメントであなたが与えた質問を考えると、現時点で私が理解していることについてのみコメントすることができます。

@Jocelynへのコメントでのクエリ

SELECT 
v2.longitude AS xa,
    /* you can use xa2 for the rest of your calcs */
2*(v2.longitude) as xa2,
v2.latitude AS ya,
v3.longitude AS xb,
    /* if you need it for the other long as well */
2*(v3.longitude) as xb2,
v3.latitude AS yb, 
(yb-ya)/(xb-xa) AS l,
    /* BTW, the (l) makes this and the next few line hard to read */
-1/l AS l_katheto,
    /* is this a negative inverse? */
(l*xa-l_katheto*$tetmimenh+ya-y1)/(l_katheto-l) AS x_tomh, 
l*(x_tomh-xa)+ya AS y_katheto,
min(
    sqrt(
        (v2.longitude-$tetmimenh)*
        (v2.longitude-$tetmimenh)+
        (v2.latit‌​ude-$tetagmenh)*
        (v2.latitude-$tetagmenh)
    ),
    sqrt(
        (v3.longitude-$tetmimenh)*
        (v3.long‌​itude-$tetmimenh)+
        (v3.latitude-$tetagmenh)*
        (v3.latitude-$tetagmenh)
    ),
    sqrt(
        ($tetmi‌​menh-x_tomh)*
        ($tetmimenh-x_tomh)+
        ($tetagmenh-y_tomh)*
        ($tetagmenh-y_tomh)
    )
) 
FROM 
segments AS v1 
JOIN points AS v2 ON v1.from_point=v2.point_id 
JOIN points AS v3 ON v3.point_id=v1.to_point