Linux学习-MySQL中truncate和delete清除表数据区别

Posted 2022-09-20 丢爸

在Linux中清除数据表中的数据可以使用truncate和delete命令
COMMIT：一旦执行COMMIT，数据将被永久保存至数据库中，意味数据不能回滚
ROLLBACK：回滚数据，一旦执行ROLLBACK，则可以实现数据回滚，回滚至最近一次COMMIT之后

对比TRUNCATE和DELETE FROM

相同点：都可以实现数据表中数据的删除，TRUNCATE删除表时会保留表结构
不同点：
TRUNCATE TABLE：一旦执行此操作，表数据全部清除，同时不能回滚
DELETE FROM：一旦执行此操作，表数据会全部删除(不带WHERE)，数据可以实现回滚。

DDL和DML

DDL的操作一旦执行，不可回滚,指令SET autocommit=false对DDL操作失效。(因为执行完DDL语句后，一定会执行一次COMMIT，而此COMMIT操作不受SET autocommit=false影响)
DML的操作默认情况下，一旦执行，也不可以回滚，但如果在执行DML之前，使用了SET autocommit=false(默认autocommit为true),则执行的DML操作可以实现回滚

delete from可回滚

mysql> select * from myemp3;
+-------------+-------------+------------------+
| employee_id | last_name   | department_name  |
+-------------+-------------+------------------+
|         200 | Whalen      | Administration   |
|         201 | Hartstein   | Marketing        |
|         202 | Fay         | Marketing        |
... ...
|         110 | Chen        | Finance          |
|         111 | Sciarra     | Finance          |
|         112 | Urman       | Finance          |
|         113 | Popp        | Finance          |
|         205 | Higgins     | Accounting       |
|         206 | Gietz       | Accounting       |
+-------------+-------------+------------------+
106 rows in set (0.01 sec)

mysql> set autocommit=false;
Query OK, 0 rows affected (0.00 sec)

mysql> delete from myemp3;
Query OK, 106 rows affected (0.01 sec)

mysql> select * from myemp3;
Empty set (0.00 sec)

mysql> rollback;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from myemp3;
+-------------+-------------+------------------+
| employee_id | last_name   | department_name  |
+-------------+-------------+------------------+
|         200 | Whalen      | Administration   |
|         201 | Hartstein   | Marketing        |
|         202 | Fay         | Marketing        |
... ...
|         110 | Chen        | Finance          |
|         111 | Sciarra     | Finance          |
|         112 | Urman       | Finance          |
|         113 | Popp        | Finance          |
|         205 | Higgins     | Accounting       |
|         206 | Gietz       | Accounting       |
+-------------+-------------+------------------+
106 rows in set (0.00 sec)

truncate table,不能回滚

mysql> select * from myemp3;
+-------------+-------------+------------------+
| employee_id | last_name   | department_name  |
+-------------+-------------+------------------+
|         200 | Whalen      | Administration   |
|         201 | Hartstein   | Marketing        |
|         202 | Fay         | Marketing        |
... ...
|         110 | Chen        | Finance          |
|         111 | Sciarra     | Finance          |
|         112 | Urman       | Finance          |
|         113 | Popp        | Finance          |
|         205 | Higgins     | Accounting       |
|         206 | Gietz       | Accounting       |
+-------------+-------------+------------------+
106 rows in set (0.00 sec)

mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)

mysql> truncate table myemp3;
Query OK, 0 rows affected (0.06 sec)

mysql> rollback;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from myemp3;
Empty set (0.00 sec)

比较(truncate和delete)

TRUNCATE 比 DELEETE速度快，且使用的系统和事务日志资源少，但TRUNCATE无事务，且不触发TRIGGER，有可能造成事故，故不建议在开发代码中使用此语句。
TRUNCATE与不带WHERE子句的DELETE语句相同