January 2005
Beginner to intermediate
928 pages
22h 14m
English
book
Understanding DB2®: Learning Visually with Examples
by Raul F. Chong, Clara Liu, Sylvia F. Qi, Dwaine R. Snow
Content preview from Understanding DB2®: Learning Visually with Examples
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16.9. The DB2 Optimizer
The DB2 optimizer, as stated in previous chapters, is the brain of DB2. The optimizer is a sophisticated and complex set of algorithms whose main objective is to calculate the fastest way to retrieve your data based on your database statistics.
The DB2 optimizer performs a number of tasks during the creation of the internal-compiled form of your SQL statements.
1. |
Parse the query.
The optimizer's first task is to analyze the SQL query to validate the syntax. If it detects any syntax errors, the optimizer stops processing, and the appropriate SQL error is returned to the application attempting to compile the SQL statement. When parsing is complete, an internal representation of the query is created. |
2. |
Check the query ... |
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