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数据管理员面试常见七个问题 1. Why is a UNION ALL faster than a UNION? The union operation, you will recall, brings two sets of data together. It will not, however, produce duplicate or redundant rows. To perform this feat of magic, a SORT operation is done on both tables. This is obviously computationally intensive, and uses significant memory as well. A UNION ALL conversely just dumps collection of both sets together in random order, not worrying about duplicates. 2. What are some advantages to using Oracle's CREATE DATABASE statement to create a new database manually? • You can script the process to include it in a set of install scripts you deliver with a product. • You can put your create database script in CVS for version control, so as you make changes or adjustments to it, you can track them like you do changes to software code. • You can log the output and review it for errors. • You learn more about the process of database creation, such as what options are available and why. 3. What are three rules of thumb to create good passwords? How would a DBA enforce those rules in Oracle? What business challenges might you encounter? | 
