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MySQL/透視表

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"透視表"或"交叉表報表"

(注意：此頁面需要維基化)

SQL 特徵函式：無需使用 "if"、"case" 或 "GROUP_CONCAT" 來實現。是的，這些函式在某些情況下有用...“if”語句有時在組合使用時會導致問題。

簡單秘訣，這也是它們幾乎在所有資料庫中都能正常工作的原因，如下所示：

  • sign (x) 分別針對值 x < 0、x = 0、x > 0 返回 -1、0、+1
  • abs( sign( x) ) 如果 x = 0 則返回 0，否則，如果 x > 0 或 x < 0 則返回 1
  • 1-abs( sign( x) ) 上述內容的補充，因為此函式僅在 x = 0 時返回 1
   Quick example:   sign(-1) = -1,  abs( sign(-1) ) = 1,  1-abs( sign(-1) ) = 0

完整示例資料

      CREATE TABLE exams (
        pkey int(11) NOT NULL auto_increment,
        name varchar(15),
        exam int,
        score int,
        PRIMARY KEY  (pkey)
      );

      insert into exams (name,exam,score) values ('Bob',1,75);
      insert into exams (name,exam,score) values ('Bob',2,77);
      insert into exams (name,exam,score) values ('Bob',3,78);
      insert into exams (name,exam,score) values ('Bob',4,80);

      insert into exams (name,exam,score) values ('Sue',1,90);
      insert into exams (name,exam,score) values ('Sue',2,97);
      insert into exams (name,exam,score) values ('Sue',3,98);
      insert into exams (name,exam,score) values ('Sue',4,99);

mysql> select * from exams;
+------+------+------+-------+
| pkey | name | exam | score |
+------+------+------+-------+
|    1 | Bob  |    1 |    75 |
|    2 | Bob  |    2 |    77 |
|    3 | Bob  |    3 |    78 |
|    4 | Bob  |    4 |    80 |
|    5 | Sue  |    1 |    90 |
|    6 | Sue  |    2 |    97 |
|    7 | Sue  |    3 |    98 |
|    8 | Sue  |    4 |    99 |
+------+------+------+-------+
8 rows in set (0.00 sec)

mysql> select name,
sum(score*(1-abs(sign(exam-1)))) as exam1,
sum(score*(1-abs(sign(exam-2)))) as exam2,
sum(score*(1-abs(sign(exam-3)))) as exam3,
sum(score*(1-abs(sign(exam-4)))) as exam4
from exams group by name;

+------+-------+-------+-------+-------+
| name | exam1 | exam2 | exam3 | exam4 |
+------+-------+-------+-------+-------+
| Bob  |    75 |    77 |    78 |    80 |
| Sue  |    90 |    97 |    98 |    99 |
+------+-------+-------+-------+-------+
2 rows in set (0.00 sec)

注意，以上透視表是用一個 select 語句建立的。

為了使技巧更清晰，讓我們分解第二個示例

mysql> select name, score, exam, exam-2, sign(exam-2), abs(sign(exam-2)), 1-abs(sign(exam-2)),
       score*(1-abs(sign(exam-2))) as exam2 from exams;
+------+-------+------+--------+--------------+-------------------+---------------------+-------+
| name | score | exam | exam-2 | sign(exam-2) | abs(sign(exam-2)) | 1-abs(sign(exam-2)) | exam2 |
+------+-------+------+--------+--------------+-------------------+---------------------+-------+
| Bob  |    75 |    1 |     -1 |           -1 |                 1 |                   0 |     0 |
| Bob  |    77 |    2 |      0 |            0 |                 0 |                   1 |    77 |
| Bob  |    78 |    3 |      1 |            1 |                 1 |                   0 |     0 |
| Bob  |    80 |    4 |      2 |            1 |                 1 |                   0 |     0 |
| Sue  |    90 |    1 |     -1 |           -1 |                 1 |                   0 |     0 |
| Sue  |    97 |    2 |      0 |            0 |                 0 |                   1 |    97 |
| Sue  |    98 |    3 |      1 |            1 |                 1 |                   0 |     0 |
| Sue  |    99 |    4 |      2 |            1 |                 1 |                   0 |     0 |
+------+-------+------+--------+--------------+-------------------+---------------------+-------+
8 rows in set (0.00 sec)

您可能認為 IF 會很乾淨，但要注意！看看以下結果（不正確！！）

mysql> select name,
if(exam=1,score,null) as exam1,
if(exam=2,score,null) as exam2,
if(exam=3,score,null) as exam3,
if(exam=4,score,null) as exam4
from exams group by name;

+------+-------+-------+-------+-------+
| name | exam1 | exam2 | exam3 | exam4 |
+------+-------+-------+-------+-------+
| Bob  |    75 |  NULL |  NULL |  NULL |
| Sue  |    90 |  NULL |  NULL |  NULL |
+------+-------+-------+-------+-------+
2 rows in set (0.00 sec)

注意：以下方法有效 - 畢竟所有的數學運算都是必要的嗎？

mysql> SELECT name,
       SUM(IF(exam=1,score,NULL)) AS exam1,
       SUM(IF(exam=2,score,NULL)) AS exam2,
       SUM(IF(exam=3,score,NULL)) AS exam3,
       SUM(IF(exam=4,score,0)) AS exam4
       FROM exams GROUP BY name;
+------+-------+-------+-------+-------+
| name | exam1 | exam2 | exam3 | exam4 |
+------+-------+-------+-------+-------+
| Bob  |    75 |    77 |    78 |    80 |
| Sue  |    90 |    97 |    98 |    99 |
+------+-------+-------+-------+-------+
2 rows in set (0.00 sec)


mysql> select name,
       sum(score*(1-abs(sign(exam-1)))) as exam1,
       sum(score*(1-abs(sign(exam-2)))) as exam2,
       sum(score*(1-abs(sign(exam-3)))) as exam3,
       sum(score*(1-abs(sign(exam-4)))) as exam4,
         sum(score*(1-abs(sign(exam- 2)))) -   sum(score*(1-abs(sign(exam- 1)))) as delta_1_2,
         sum(score*(1-abs(sign(exam- 3)))) -   sum(score*(1-abs(sign(exam- 2)))) as delta_2_3,
         sum(score*(1-abs(sign(exam- 4)))) -   sum(score*(1-abs(sign(exam- 3)))) as delta_3_4
       from exams group by name;
+------+-------+-------+-------+-------+-----------+-----------+-----------+
| name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 |
+------+-------+-------+-------+-------+-----------+-----------+-----------+
| Bob  |    75 |    77 |    78 |    80 |         2 |         1 |         2 |
| Sue  |    90 |    97 |    98 |    99 |         7 |         1 |         1 |
+------+-------+-------+-------+-------+-----------+-----------+-----------+
2 rows in set (0.00 sec)

上面的 delta_1_2 顯示了第一次和第二次考試之間的差異，數字為正，因為 Bob 和 Sue 的成績在每次考試中都有所提高。在這裡計算增量表明可以比較兩行，而不是列，而列可以用標準 SQL 語句輕鬆完成，但在原始表中則是行。

mysql>select name,
sum(score*(1-abs(sign(exam-1)))) as exam1,
sum(score*(1-abs(sign(exam-2)))) as exam2,
sum(score*(1-abs(sign(exam-3)))) as exam3,
sum(score*(1-abs(sign(exam-4)))) as exam4,
  sum(score*(1-abs(sign(exam- 2)))) -   sum(score*(1-abs(sign(exam- 1)))) as delta_1_2,
  sum(score*(1-abs(sign(exam- 3)))) -   sum(score*(1-abs(sign(exam- 2)))) as delta_2_3,
  sum(score*(1-abs(sign(exam- 4)))) -   sum(score*(1-abs(sign(exam- 3)))) as delta_3_4,

  sum(score*(1-abs(sign(exam- 2)))) -   sum(score*(1-abs(sign(exam- 1))))  +
  sum(score*(1-abs(sign(exam- 3)))) -   sum(score*(1-abs(sign(exam- 2))))  +
  sum(score*(1-abs(sign(exam- 4)))) -   sum(score*(1-abs(sign(exam- 3))))  as TotalIncPoints
  from exams group by name;

+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+
| name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 | TotalIncPoints |
+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+
| Bob  |    75 |    77 |    78 |    80 |         2 |         1 |         2 |              5 |
| Sue  |    90 |    97 |    98 |    99 |         7 |         1 |         1 |              9 |
+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+
2 rows in set (0.00 sec)

TotalIncPoints 顯示增量的總和。

select name,
sum(score*(1-abs(sign(exam-1)))) as exam1,
sum(score*(1-abs(sign(exam-2)))) as exam2,
sum(score*(1-abs(sign(exam-3)))) as exam3,
sum(score*(1-abs(sign(exam-4)))) as exam4,
  sum(score*(1-abs(sign(exam- 2)))) -   sum(score*(1-abs(sign(exam- 1)))) as delta_1_2,
  sum(score*(1-abs(sign(exam- 3)))) -   sum(score*(1-abs(sign(exam- 2)))) as delta_2_3,
  sum(score*(1-abs(sign(exam- 4)))) -   sum(score*(1-abs(sign(exam- 3)))) as delta_3_4,


  sum(score*(1-abs(sign(exam- 2)))) -   sum(score*(1-abs(sign(exam- 1))))  +
  sum(score*(1-abs(sign(exam- 3)))) -   sum(score*(1-abs(sign(exam- 2))))  +
  sum(score*(1-abs(sign(exam- 4)))) -   sum(score*(1-abs(sign(exam- 3))))  as TotalIncPoints,

(sum(score*(1-abs(sign(exam-1)))) +
sum(score*(1-abs(sign(exam-2)))) +
sum(score*(1-abs(sign(exam-3)))) +
sum(score*(1-abs(sign(exam-4)))))/4 as AVG

from exams group by name;

+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+
| name | exam1 | exam2 | exam3 | exam4 | delta_1_2 | delta_2_3 | delta_3_4 | TotalIncPoints | AVG   |
+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+
| Bob  |    75 |    77 |    78 |    80 |         2 |         1 |         2 |              5 | 77.50 |
| Sue  |    90 |    97 |    98 |    99 |         7 |         1 |         1 |              9 | 96.00 |
+------+-------+-------+-------+-------+-----------+-----------+-----------+----------------+-------+
2 rows in set (0.00 sec)

可以將 Total Increasing Point TotalIncPoints 與 AVG 組合起來。實際上，可以將所有示例資料切片組合到一個 SQL 語句中，這為在頁面上顯示資料提供了更多選擇

select name,
sum(score*(1-abs(sign(exam-1)))) as exam1,
sum(score*(1-abs(sign(exam-2)))) as exam2,
sum(score*(1-abs(sign(exam-3)))) as exam3,
sum(score*(1-abs(sign(exam-4)))) as exam4,

(sum(score*(1-abs(sign(exam-1)))) +
sum(score*(1-abs(sign(exam-2)))))/2  as AVG1_2,

(sum(score*(1-abs(sign(exam-2)))) +
sum(score*(1-abs(sign(exam-3)))))/2 as AVG2_3,

(sum(score*(1-abs(sign(exam-3)))) +
sum(score*(1-abs(sign(exam-4)))))/2 as AVG3_4,

(sum(score*(1-abs(sign(exam-1)))) +
sum(score*(1-abs(sign(exam-2)))) +
sum(score*(1-abs(sign(exam-3)))) +
sum(score*(1-abs(sign(exam-4)))))/4 as AVG

from exams group by name;

+------+-------+-------+-------+-------+--------+--------+--------+-------+
| name | exam1 | exam2 | exam3 | exam4 | AVG1_2 | AVG2_3 | AVG3_4 | AVG   |
+------+-------+-------+-------+-------+--------+--------+--------+-------+
| Bob  |    75 |    77 |    78 |    80 |  76.00 |  77.50 |  79.00 | 77.50 |
| Sue  |    90 |    97 |    98 |    99 |  93.50 |  97.50 |  98.50 | 96.00 |
+------+-------+-------+-------+-------+--------+--------+--------+-------+
2 rows in set (0.00 sec)

考試分數與移動平均值一起列出...同樣，這一切都用一個 select 語句完成。

"交叉表"或反規範化資料以顯示統計資訊的優秀文章：https://dev.mysql.com.tw/tech-resources/articles/wizard/print_version.html

ADOdb (PHP) 可以使用 PivotTableSQL() 生成透視表。

對於 Perl，請檢視 DBIx-SQLCrosstab。

檢索自 "https://wikibook.tw/w/index.php?title=MySQL/Pivot_table&oldid=3266959"
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