Oracle database Development Face Questions

Recently participated in 4, 5 interviews, summed up the competition in the Oracle development post most frequently asked what questions:

1. What is the difference between delete and truncate?

1) Truncate is a DDL statement, and delete is a DML statement;

2) Truncate speed is much faster than delete;

The reason is that when we perform a delete operation, all table data is copied to the rollback table space first, and the amount of data varies over time. While truncate is directly deleting data, it does not go into the rollback table space.

3) Connect (2) This also causes the delete data after we can run rollback for data rollback, while truncate is permanently deleted cannot rollback;

4) The truncate operation does not touch the delete trigger on the publication, and delete will trigger normally;

5) Truncate statement cannot take a where condition means that only all data can be deleted, and delete can delete some data;

6) The TRUNCATE operation resets the table's high watermark (higher water Mark), and delete does not.

PS: About high watermark HWM knowledge Clear reference article: http://blog.csdn.net/indexman/article/details/25910255

2, explain the three paradigms of the database?

Please refer to: http://blog.csdn.net/indexman/article/details/19907731

Please look forward to!

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Dylan presents.