移位值向下一個表中的鏈

Question

假設我有以下結果從一個MySQL數據庫表中設置：

+----+------+-------+ 
| ID | type | value | 
+----+------+-------+ 
| 8 | A | 1435 | 
| 9 | B | 7348 | 
| 10 | A | 1347 | 
| 11 | A | 3478 | 
| 12 | A | 4589 | 
| 13 | B | 6789 | 
+----+------+-------+ 

我想刪除行ID 8和外地「值」推值按照這種方式，每一行都具有先前條目的值，但隻影響字段'type'與被刪除的行相同的那一行（在這種情況下爲'A'）。

也就是說，刪除行ID 8應最終產生以下：

+----+------+-------+ 
| ID | type | value | 
+----+------+-------+ 
| - | - | - | * 
| 9 | B | 7348 | | 
| 10 | A | 1435 | * | 
| 11 | A | 1347 | * | 
| 12 | A | 3478 | * | 
| 13 | B | 6789 | V 
+----+------+-------+ 

ID 10已從ID 8繼承的值，然後從ID 10 ID，依此類推11所繼承。不過請注意，類型'B'的行不受影響。

所以問題：有沒有辦法執行這個值的「轉移」，而不必逐一查詢和更新每一行？在一個理想的世界中，我會做一個查詢來完成移位，然後再執行另一個查詢來刪除行，但我不確定這是否可行。

（此外，我寧可不使用觸發器，因爲我打算在應用程序中封裝了所有的應用程序邏輯）

Answer 1

SET @remove_id = 8; 

SELECT ID, type, value FROM (
    SELECT ID, 
      type, 
      CAST(IF(type <> @type OR ISNULL(@val), value, @val) AS UNSIGNED) 
      AS value, 
      @type := IF(ID = @remove_id, type, @type), 
      @val := IF(type = @type, value, @val) 
    FROM  my_table JOIN (SELECT @type := NULL, @val := NULL) AS z 
    ORDER BY ID ASC 
) AS t 
WHERE ID <> @remove_id 

看到它的sqlfiddle。

---

UPDATE

我沒有意識到你其實是想更新基礎表。爲此，您可以使用一些輕微的hackery在UPDATE語句中有效地執行相同的操作（不能直接分配給用戶變量，因此請將分配給它的新值的串聯和從獲取新分配的用戶變量的前0個字符）：

SET @remove_id = 8, @type = NULL, @val = NULL; 

UPDATE my_table SET 
    value = IF(
    type <> @type OR ISNULL(@val), 
    value, 
    CONCAT(@val, LEFT(@val := value, 0)) 
), 
    type = CONCAT(type, LEFT(
    @type := IF(
     ID <> @remove_id, 
     @type, 
     CONCAT(type, LEFT(@val := value, 0)) 
    ) 
    , 0)) 
ORDER BY ID ASC; 

DELETE FROM my_table WHERE ID = @remove_id; 

請參閱sqlfiddle。

Answer 2

我會建議你使用InnoDB表，所以你可以在一個事務中運行2個查詢。 我這樣做：

Step 1: Start a transaction on the table 
Step 2: Get the record that is to be deleted (e.g. ID #8) 
Step 3: Issue a query DELETE FROM tablename WHERE `ID`=$record_id 
Step 4: Issue a query UPDATE tablename SET `value`='former_value' WHERE `type`='former_type' LIMIT 1 
Step 5: if all operations were successful, commit the transaction else rollback 
Step 6: End the transaction 

希望這有助於

Answer 3

使用窗口/分析功能很容易完成此任務。由於MySQL沒有這些，所以可以用下面的限制來模擬它們：

• 你應該有一個唯一的字段進行排序。

我爲此使用了id。

下面的查詢將enumarte每一行的表，使用type作爲分區指標：

SELECT t.id, t.type, t.value, 
    (SELECT count(*) FROM testbed WHERE type = t.type AND id <= t.id) AS rownum 
    FROM testbed t 
ORDER BY t.type, t.id; 

我只對公開程度增加ORDER BY，在最終的查詢不是必需的。

下一頁查詢允許你加入2周的結果，並有辦法「移值」所需要的方式：

SELECT c.id AS c_id, c.type AS c_type, c.value AS c_value, 
     p.id AS p_id, p.type AS p_type, p.value AS p_value 
    FROM (SELECT t.id, t.type, t.value, 
       (SELECT count(*) FROM testbed 
       WHERE type = t.type AND id <= t.id) AS rownum 
      FROM testbed t) AS c 
    LEFT JOIN (SELECT t.id, t.type, t.value, 
        (SELECT count(*) FROM testbed 
         WHERE type = t.type AND id <= t.id) AS rownum 
       FROM testbed t) AS p 
     ON c.type = p.type AND c.rownum = p.rownum + 1 
ORDER BY c.type, c.id; 

最後，你的任務是用以下2個查詢來完成，UPDATE和DELETE：

UPDATE testbed AS t 
JOIN (
    SELECT c.id AS c_id, c.type AS c_type, c.value AS c_value, 
     p.id AS p_id, p.type AS p_type, p.value AS p_value 
    FROM (SELECT t.id, t.type, t.value, 
       (SELECT count(*) FROM testbed 
        WHERE type = t.type AND id <= t.id) AS rownum 
      FROM testbed t) AS c 
    LEFT JOIN (SELECT t.id, t.type, t.value, 
         (SELECT count(*) FROM testbed 
         WHERE type = t.type AND id <= t.id) AS rownum 
       FROM testbed t) AS p 
      ON c.type = p.type AND c.rownum = p.rownum + 1 
) AS s 
    ON t.id = s.c_id 
    SET t.value = s.p_value 
WHERE t.value = 'A'; -- you can use more complex predicate(s) here 

DELETE FROM testbed WHERE id = 8; -- make sure both predicate(s) match 

您可以在SQL Fiddle（不是更新）上檢查此查詢。