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MySQL TRUNCATE 和 DELETE 指令有什麼不同?

WBOY
WBOY轉載
2023-09-12 14:13:02879瀏覽

MySQL TRUNCATE 和 DELETE 命令有什么区别?

眾所周知,TRUNCATE 會刪除所有行,而不會從資料庫中刪除資料表的結構。可以藉助 DELETE 指令完成相同的工作,從表中刪除所有行。但這兩個指令之間的 PRIMARY KEY AUTO_INCRMENT 重新初始化有顯著差異。

假設一列定義了具有PRIMARY KEY CONSTRAINT 的AUTO_INCRMENT,那麼在使用DELETE 命令刪除所有行時將不會重新初始化初始化表,即在輸入新行時,AUTO_INCREMENT 數字將從最後插入的行之後開始。相反,在使用 TRUNCATE 時,表將像新建立的表一樣重新初始化。這意味著使用 TRUNCATE 命令並插入新行後,AUTO_INCRMENT 數字將從 1 開始。

範例

以下範例將示範上述概念 -

mysql> Create table Testing(Id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, Name Varchar(20));
Query OK, 0 rows affected (0.15 sec)

mysql> Insert into testing(Name) values('Gaurav'),('Rahul'),('Aarav'),('Yashraj'),('Manak');
Query OK, 5 rows affected (0.09 sec)
Records: 5 Duplicates: 0 Warnings: 0

mysql> Select * from testing;

+----+---------+
| Id | Name    |
+----+---------+
| 1  | Gaurav  |
| 2  | Rahul   |
| 3  | Aarav   |
| 4  | Yashraj |
| 5  | Manak   |
+----+---------+

5 rows in set (0.00 sec)

mysql> Delete from testing where id >=4;
Query OK, 2 rows affected (0.04 sec)

mysql> Select * from testing;

+----+--------+
| Id | Name   |
+----+--------+
| 1  | Gaurav |
| 2  | Rahul  |
| 3  | Aarav  |
+----+--------+

3 rows in set (0.00 sec)

mysql> Insert into testing(Name) values('Harshit'),('Lovkesh');
Query OK, 2 rows affected (0.06 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> Select * from testing;

+----+---------+
| Id | Name    |
+----+---------+
| 1  | Gaurav  |
| 2  | Rahul   |
| 3  | Aarav   |
| 6  | Harshit |
| 7  | Lovkesh |
+----+---------+

5 rows in set (0.00 sec)

mysql> Truncate table testing;
Query OK, 0 rows affected (0.10 sec)

mysql> Insert into testing(Name) values('Harshit'),('Lovkesh'),('Ram'),('Gaurav');
Query OK, 4 rows affected (0.11 sec)
Records: 4 Duplicates: 0 Warnings: 0

mysql> Select * from testing;

+----+---------+
| Id | Name    |
+----+---------+
| 1  | Harshit |
| 2  | Lovkesh |
| 3  | Ram     |
| 4  | Gaurav  |
+----+---------+

4 rows in set (0.00 sec)

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