Solved

Mysql complex update syntax

Posted on 2010-09-21
3
507 Views
Last Modified: 2012-05-10
I have a table with pairs of records, each can be tied together via an ID number.  Each pair has a time value where 1 record might be the same or later in time than its pair.  I want to update the check_time field where the newer time = 'Y' and the older time can stay the default 'N'.  If the times are the same, I want to use a different field that happens to be boolean (0,1) to determine the check_time field, something like if boolean_field = 0 set check_time = 'Y'

I'll try to create sample table data in code section.
record | shared_id | boolean_field | time | check_time
1      |  25       |  0            | 3:01 | Y
2      |  25       |  1            | 3:00 | N

Open in new window

0
Comment
Question by:mcgilljd
3 Comments
 
LVL 58

Accepted Solution

by:
cyberkiwi earned 500 total points
ID: 33730342
Because of your complex tiebreak - time, then boolean_field, a 3 level subquery is required.
Please see below.
update qm
left join
(
select q3.record
from (
	select q2.shared_id, MT.maxtime, Min(q2.boolean_field) minbool
	from (
		select shared_id, max(time) maxtime
		from qm q1
		group by shared_id) MT
	inner join qm q2 on q2.shared_id=MT.shared_id and q2.time=MT.maxtime
	group by q2.shared_id, MT.maxtime) mb
inner join qm q3 on mb.shared_id=q3.shared_id and mb.maxtime=q3.time and mb.minbool=q3.boolean_field
) qx on qx.record=qm.record
set check_time = case when qx.record is null then 'N' else 'Y' end

Open in new window

0
 
LVL 59

Expert Comment

by:Kevin Cross
ID: 33738955
Here is another approach that might help:

create table qm(record int,shared_id int,boolean_field tinyint(1),`time` time, check_time char(1));

insert into qm
values(1, 25, 0, '03:01', 'N'),
(2, 25, 1, '03:00', 'N');

Might be same was what cyberkiwi is doing above, I haven't checked...
update qm q1
join (
   select shared_id, max(`time`) as max_time
   from qm 
   group by shared_id
) q3 on q1.`time` = q3.max_time
   and q3.shared_id = q1.shared_id
join qm q2 on q2.shared_id = q1.shared_id
   and q2.record <> q1.record
set q1.check_time = 
   case 
      when (q1.`time` > q2.`time`) 
        or (q1.`time` = q2.`time` and q1.boolean_field = 0) 
        then 'Y' 
      else 'N' 
   end
;

Open in new window

0
 

Author Closing Comment

by:mcgilljd
ID: 33744854
Wow!
That was awesome!
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

This article describes some very basic things about SQL Server filegroups.
Using SQL Scripts we can save all the SQL queries as files that we use very frequently on our database later point of time. This is one of the feature present under SQL Workshop in Oracle Application Express.
Video by: Steve
Using examples as well as descriptions, step through each of the common simple join types, explaining differences in syntax, differences in expected outputs and showing how the queries run along with the actual outputs based upon a simple set of dem…
Polish reports in Access so they look terrific. Take yourself to another level. Equations, Back Color, Alternate Back Color. Write easy VBA Code. Tighten space to use less pages. Launch report from a menu, considering criteria only when it is filled…

809 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question