[英]What's the best way to query for position changes?
我有一張要顯示的結果表:
| change | position | name | score |
|----------------------------------|
| - | 1 | Bob | 10 |
| +1 | 2 | Tom | 8 |
| -1 | 3 | Sam | 7 |
|----------------------------------|
更改列反映了人的位置移動,因此從第三名到第二名的移動是+1,從第二名到第三名的移動是-1等。因此在上面的示例中,由於湯姆上一場超越了薩姆。
我可以編寫一條提供結果(包括“更改”列)的SQL語句嗎?
現在,我正在編寫兩個查詢來執行此操作。 我得到不包括最新游戲的分數,然后得到包含最新游戲的分數,並在我繪制表格時進行比較。
例:
以前的游戲結果 :
SELECT p.name, p.id, SUM(g.points) AS score
FROM players p INNER JOIN games g ON p.id=g.player_id
WHERE g.id<5
ORDER BY score DESC
然后將它們存儲在數組中:
$i=1;
while($row = mysql_fetch_assoc($results){
$prevPositions[$row['id']] = $i++;
//render row
}
所有游戲結果 :
SELECT p.name, SUM(g.points) AS score
FROM players p INNER JOIN games g ON p.id=g.player_id
ORDER BY score DESC
然后計算呈現表時的區別:
$i=1;
while($row = mysql_fetch_assoc($results){
$change = $prevPositions[$row['id']] - $i++;
//render row
}
這很好用-但是如果我只使用一個語句而不是兩個語句,我會感覺更好。
試試這個:
SELECT (S0.Rank - S1.Rank) As Change, S1.Rank As Position, S1.name, S1.score
FROM (SELECT p.name, p.id, SUM(g.points) AS score, @rank1:=@rank1+1 As rank
FROM (SELECT @rank1:=0) r, players p
INNER JOIN games g ON p.id=g.player_id
ORDER BY score DESC) S1
JOIN
(SELECT p.id, SUM(g.points) AS score, @rank2:=@rank2+1 As rank
FROM (SELECT @rank2:=0) r, players p
INNER JOIN games g ON p.id=g.player_id
WHERE g.id<5
ORDER BY score DESC) S0
ON S0.id = s1.id
(我還沒有測試!)
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