tailieunhanh - Joe Celko s SQL for Smarties - Advanced SQL Programming P69

Joe Celko s SQL for Smarties - Advanced SQL Programming P69. In the SQL database community, Joe Celko is a well-known columnist and purveyor of valuable insights. In Joe Celko's SQL for Smarties: Advanced SQL Programming, he picks up where basic SQL training and experience leaves many database professionals and offers tips, techniques, and explanations that help readers extend their capabilities to top-tier SQL programming. Although Celko denies that the book is about database theory, he nevertheless alludes to theory often to buttress his practical points. This title is not for novices, as the author points out. Instead, its intended. | 652 CHAPTER 29 TEMPORAL QUERIES 2005-05-11 2005-05-11 2005-05-11 2005-05-11 2005-05-11 03 00 03 01 03 02 03 03 03 04 2005-05-11 03 01 9 2005-05-11 03 02 9 2005-05-11 03 03 8 2005-05-11 03 04 8 2005-05-11 03 05 8 I want to be able to group this data so that it looks like this start_time end_time cal_value 2005-05-11 02 52 2005-05-11 02 57 2005-05-11 03 02 2005-05-11 02 57 2005-05-11 03 02 2005-05-11 03 05 8 9 8 Background The table being selected from is updated every minute with a new calibration value. The calibration value can change from minute to minute. I want a select statement that will sum up the start of the cal_value and the end of the calibration value before it changes. SELECT MIN start_time AS start_time MAX end_time AS end_time cal_value FROM SELECT MIN FROM Calibrations AS C1 LEFT OUTER JOIN Calibrations AS C2 ON AND GROUP BY AS T start_time end_time cal_value x_time GROUP BY cal_value x_time Missing Times in Contiguous Events Consider the following simple table which we will use to illustrate how to handle missing times in events. CREATE TABLE Events event_id CHAR 2 NOT NULL PRIMARY KEY start_date DATE Time Series 653 end_date DATE CHECK start_date end_date INSERT INTO Events VALUES A 2003-01-01 2003-12-31 B 2004-01-01 2004-01-31 C 2004-02-01 2004-02-29 D 2004-02-01 2004-02-29 Due to circumstances beyond our control the end_date column may contain a null instead of a valid date. Imagine that we had B 2004-01-01 null as a row in the table. One reasonable solution is to populate the missing end_date with the start_date -1 day of the next period. This is easy enough. UPDATE Events SET end_date SELECT MIN - INTERVAL 1 DAY FROM Events AS E1 WHERE .