October 2002
Beginner
864 pages
18h 41m
English
Content preview from Sams Teach Yourself SQL in 21 Days, Fourth Edition
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Q&A
| Q1: | If the data within my table is already in sorted order, why should I use an index on that table? |
| A1: | An index still gives you a performance benefit by looking quickly through key values in a tree. The index can locate records faster than a direct access search through each record within your database. Remember—the SQL query processor doesn't necessarily know that your data is in sorted order. |
| Q2: | Can I create an index that contains fields from multiple tables? |
| A2: | No, you cannot. However, Oracle, for instance, allows you to create a cluster. You can place tables within a cluster and create cluster indexes on fields that are common to the tables. This implementation is the exception, not the rule, so be sure to study your documentation on ... |
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