如何在AVG功能中使用別名

Question

我在下面有下面的代碼，我試圖獲得3列的AVG。

SELECT 
    (SUM(score) * .3) As score_a, 
    (SUM(score) * .6) As score_b, 
    (SUM(score) * .8) As score_c 

    --now I want to get the AVG of the above scores 
    AVG(score_a + score_b + score_c) As avg_score 
FROM score_table 

但這不起作用。我收到的錯誤是「無效的列名稱score_a」。 我使用SQL Server 2008

Answer 1

AVG()是一個聚集函數，它的值從多個行並給出了它們的平均值。

您正在設法通過3 列。

我是你的具體情況，可以用代數來完成。

SELECT 
    (SUM(score) * .3)      As score_a, 
    (SUM(score) * .6)      As score_b, 
    (SUM(score) * .8)      As score_c, 
    (SUM(score) * ((0.3 + 0.6 + .8)/3.0)) As score_avg 
FROM 
    score_table 

在更廣義的情況下，你的事實，你不能引用剛在另一列定義的列限制...

SELECT 
    a + 1  AS inc_a, 
    inc_a * 2 AS this_is_invalid 
FROM 
    your_table 

你會要麼需要重複自己，或使用子查詢...

重複

SELECT 
    (SUM(score) * .3)             As score_a, 
    (SUM(score) * .6)             As score_b, 
    (SUM(score) * .8)             As score_c, 
    ((SUM(score) * .3) + (SUM(score) * .3) + (SUM(score) * .3))/3.0 As score_avg 
FROM 
    score_table 

子查詢

SELECT 
    score_a, 
    score_b, 
    score_c, 
    (score_a + score_b + score_c)/3.0 AS score_avg 
FROM 
(
    SELECT 
    (SUM(score) * .3)            As score_a, 
    (SUM(score) * .6)            As score_b, 
    (SUM(score) * .8)            As score_c 
    FROM 
    score_table 
) 
    AS data 

Answer 2

你能嘗試：

SELECT 
    (SUM(score) * .3) As score_a, 
    (SUM(score) * .6) As score_b, 
    (SUM(score) * .8) As score_c, 
    AVG(score_a + score_b + score_c) As avg_score 
FROM score_table 

，看看是否適合你？

Answer 3

有手動做平均的蠻力方法，但它不會像您添加列一樣進行縮放。 :)

SELECT CAST((score_a + score_b + score_c)/3 AS DECIMAL(20,2)) As avg_score, 
     score_a, 
     score_b, 
     score_c 
FROM (
    SELECT (SUM(score) * .3) As score_a, 
      (SUM(score) * .6) As score_b, 
      (SUM(score) * .8) As score_c 
    FROM score_table 
    GROUP BY userid, gameid --Whatever you're grouping by here! 
)