數值運算

Snowflake 的資料型別與函式

Jake Roach

Field Data Engineer

數值運算

三種數值計算與操作。

比較數值

比較運算子可用來比較或評估多個值

=, 兩個值是否為「相等」？
!=, 兩個值是否「不相等」？
<, 是否「小於」另一個值？
>, 是否「大於」另一個值？
<= 小於「或」等於
>=, 大於「或」等於

                回傳 `true` 或 `false`！

        1 = 1,   -- true

        1 != 1,   -- false

        1 < 2,    -- true

        1 > 2,    -- false

        1 <= 2,    -- true

        2 >= 2    -- true

               ...

WHERE 1 = 1   -- Filter records

Snowflake 的算術運算

SELECT

    <#> + <#>,        -- 2 + 2  ->  4
    <field> - <#>,    -- 4 - 1  ->  3
    <field> * <#>,    -- 3 * 2  ->  6
    <field> / <#>,    -- 9 / 3  ->  3

                ...

可在 # 與 field 的各種排列間進行運算

算術運算子可對數值做「運算」

+，加法
-，減法
*，乘法
/，除法

算術運算

SELECT
    student_name, exam_score,


    exam_score + 10 AS add_points,      -- Add 10 points to each student's grade

    exam_score * curve AS curved,       -- Curve the grade by 10%

    exam_score / 2 AS weighted          -- Reduce the weight of the test


FROM STUDENTS.grades;

              student_name  |   exam_score   |  add_points  |  curved  |  weighted  
             -------------- | -------------- | ------------ | -------- | ----------
               Ryan         |       78       |      88      |   85.8   |     39
               Tatiana      |       89       |      99      |   97.9   |    44.5
               Pankaj       |       74       |      84      |   81.4   |     37

聚合函式產生摘要資料

GROUP BY 聚合紀錄示意圖。

聚合函式

 SELECT

     <1>,


     SUM(<field>),  -- Returns the total of a column

     AVG(<field>)   -- Finds the average value of a column


 FROM ...


 GROUP BY <1>;

「非聚合欄位」必須 GROUP BY！

GROUP BY ALL

聚合函式

SELECT
    exam_name,

    SUM(correct_answers) AS total_correct_answers,      -- Total # correct
    AVG(exam_score) AS avg_exam_score,                  -- Average exam score


    ROUND(AVG(exam_score), 1) AS rounded_exam_score     -- ROUND(<value>, <n>)


FROM STUDENTS.grades
GROUP BY exam_name;  -- GROUP BY to aggregate records, otherwise error

ROUND() 需要要四捨五入的值，以及小數點後要保留的位數

聚合函式

   exam_name    |  total_correct_answers  |  avg_exam_score  |  rounded_avg_exam_score 
  ------------- | ----------------------- | ---------------- | ------------------------ 
   Calculus I   |           871           |      89.11111    |           89.1     
   Biology      |           776           |      87.47777    |           87.5
   English III  |           541           |      91.33333    |           91.3
   Python       |          1179           |      92.78787    |           92.8
   Finance      |           349           |      96.14156    |           96.1

以上值使用下列方式產生：

SUM(correct_answers)
AVG(exam_score)
ROUND(AVG(exam_score), 2)

一起來練習吧！

Snowflake 的資料型別與函式