Questions about oracle Database Development

Source: Internet
Author: User

I recently attended 4 or 5 interviews to summarize the most common questions about competing for oracle development jobs:

1. What is the difference between delete and truncate?

1) truncate is a DDL statement and delete is a DML statement;

2) truncate is much faster than delete;

The reason is: When we perform the delete operation, all table data is first copied to the rollback tablespace, and the data size takes different time. However, truncate directly deletes data and does not roll back the tablespace.

3) connect to (2). This causes the delete data to be rolled back by running rollback, while truncate means permanent deletion and cannot be rolled back;

4) The truncate operation will not trigger the delete trigger on the table, but the delete operation will trigger normally;

5) The truncate statement does not contain the where condition, which means that only all data can be deleted, while the delete statement can delete some data;

6) The truncate operation resets the table's High Water Mark, but the delete operation does not.

Ps: high water level line HWM knowledge clear reference:

2. What is the three paradigm of database?


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