行號和組通過使用 Select 語句中的變數

假設我們有一個表 team_person 如下：

+======+===========+
| `team` |    person |
+======+===========+
|   A  |      John |
+------+-----------+
|   B  |     Smith |
+------+-----------+
|   A  |    Walter |
+------+-----------+
|   A  |     Louis |
+------+-----------+
|   C  | Elizabeth |
+------+-----------+
|   B  |     Wayne |
+------+-----------+

CREATE TABLE team_person AS SELECT 'A' team, 'John' person
UNION ALL  SELECT 'B' team,  'Smith' person
UNION ALL  SELECT 'A' team,  'Walter' person
UNION ALL  SELECT 'A' team,  'Louis' person
UNION ALL  SELECT 'C' team,  'Elizabeth' person
UNION ALL  SELECT 'B' team,  'Wayne' person;

要選擇帶有附加 row_number 列的表 team_person，也可以

SELECT @row_no := @row_no+1 AS row_number, team, person
FROM team_person, (SELECT @row_no := 0) t;

要麼

SET @row_no := 0;
SELECT  @row_no := @row_no + 1 AS row_number, team, person
FROM team_person;

將輸出以下結果：

+============+======+===========+
| row_number | team |    person |
+============+======+===========+
|          1 |   A  |      John |
+------------+------+-----------+
|          2 |   B  |     Smith |
+------------+------+-----------+
|          3 |   A  |    Walter |
+------------+------+-----------+
|          4 |   A  |     Louis |
+------------+------+-----------+
|          5 |   C  | Elizabeth |
+------------+------+-----------+
|          6 |   B  |     Wayne |
+------------+------+-----------+

最後，如果我們想通過列 team 獲取 row_number 組

SELECT @row_no := IF(@prev_val = t.team, @row_no + 1, 1) AS row_number
   ,@prev_val := t.team AS team
   ,t.person  
FROM team_person t,
  (SELECT @row_no := 0) x,
  (SELECT @prev_val := '') y
ORDER BY t.team ASC,t.person DESC; 

+============+======+===========+
| row_number | team |    person |
+============+======+===========+
|          1 |   A  |    Walter |
+------------+------+-----------+
|          2 |   A  |     Louis |
+------------+------+-----------+
|          3 |   A  |      John |
+------------+------+-----------+
|          1 |   B  |     Wayne |
+------------+------+-----------+
|          2 |   B  |     Smith |
+------------+------+-----------+
|          1 |   C  | Elizabeth |
+------------+------+-----------+