July 2010
Intermediate to advanced
840 pages
16h 33m
English
Content preview from Joe Celko's SQL for Smarties, 3rd Edition
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24.4. Bound Queries
Another form of query asks whether there is an overall trend between two points in time bounded by a low value and a high value in the sequence of data. This is easier to show with an example. Let us assume that we have data on the selling prices of a stock in a table. We want to find periods of time when the price was generally increasing.
Consider this data:
MyStock sale_date price ====================== '2006-12-01' 10.00 '2006-12-02' 15.00 '2006-12-03' 13.00 '2006-12-04' 12.00 '2006-12-05' 20.00
The stock was generally increasing in all the periods that began on December 1 or ended on December 5—that is, it finished higher at the ends of those periods, in spite of the slump in the middle. A query for this problem is: ...
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