March 2007
Intermediate to advanced
488 pages
13h 46m
English
book
OnDemand SQL Performance Analysis Simplified on DB2 for i5/OS in V5R4
by Hernando Bedoya, Jaime Gaug, James Kerl, Ser Ser NG, Jose Cardoso dos Santos
Content preview from OnDemand SQL Performance Analysis Simplified on DB2 for i5/OS in V5R4
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Chapter 12. Tips to proactively prevent SQL performance problems 413
performed by CQE, while in the second case, an index probe in combination with a table
probe is executed by SQE.
Figure 12-1 Comparing the use of logical and physical files in select statements
12.2.2 Avoid using SELECT * in your select statements
When reading a record with native I/O, all fields and field values are always moved into
memory. If you have tables with a lot of columns and you only need information from a few, a
lot of unnecessary information must be loaded. With SQL, you can select only the columns
that you need to satisfy the data request.
If you specify the required ...
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