[Last Call] Learn about multicloud storage options and how to improve your company's cloud strategy. Register Now


What is wrong with this MySQL statement?

Posted on 2011-09-17
Medium Priority
Last Modified: 2012-05-12
The statement below does not give an error code, but it does not compute the TIMEDIFF:

"UPDATE Stop_times, Start_times
SET Stop_times.Project_Charge_Time=TIMEDIFF(Stop_times.STOPid,Start_times.STARTid)
WHERE Start_times.PROJECTid = Stop_times.PROJECTid

but if you delete the update and modify it to a select statement like '/**UPDATE Stop_times, Start_times
SET Stop_times.Project_Charge_Time=/**/  SELECT TIMEDIFF(Stop_times.STOPid,Start_times.STARTid)
FROM Stop_times, Start_times
WHERE Start_times.PROJECTid = Stop_times.PROJECTid

it computes the time difference correctly
Question by:ToreJohn
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 3
LVL 60

Expert Comment

by:Kevin Cross
ID: 36554322
Hi. You said it does not throw an error; therefore, how are you judging that it did not compute?
LVL 60

Expert Comment

by:Kevin Cross
ID: 36554337
The syntax you have looks fine, so suspect something else. For example, by naming convention, I would not expect the actual time values to be in a column STARTid or STOPid. When I see that I think AUTO_INCREMENT or INT fields that are keys to a table. Try the below syntax ensuring that the columns in TIMEDIFF are indeed DATETIME columns. Since you said this works in SELECT, that may be the STARTid and STOPid, but may be worth double checking.

UPDATE Stop_times stp
JOIN Start_times strt 
    ON strt.PROJECTid = stp.PROJECTid
   AND strt.EMPLOYid = stp.EMPLOYid
SET stp.Project_Charge_Time = TIMEDIFF(stp.STOPdatetime, strt.STARTdatetime)

Open in new window


Author Comment

ID: 36554366
I can see that it does not work because stp.Project_Charge_Time is 0000-00-00 00:00:00 also after running the query. Your alternative code gives the same result. (When I modified stp.STOPdatetime to STOPid and the same for STARTid)
NFR key for Veeam Backup for Microsoft Office 365

Veeam is happy to provide a free NFR license (for 1 year, up to 10 users). This license allows for the non‑production use of Veeam Backup for Microsoft Office 365 in your home lab without any feature limitations.

LVL 60

Expert Comment

by:Kevin Cross
ID: 36554372
Wait. Project_Charge_Time is a datetime?
Remember TIMEDIFF is given you a difference in time values. It is not resulting in a datetime value. Please show the table structure(s) and some sample data with what you expect the final results to be.

Author Comment

ID: 36554431
Yes and Thanks.
I used datetime as the format for the output. Changing the format did the trick
LVL 60

Accepted Solution

Kevin Cross earned 2000 total points
ID: 36554441
You are welcome!

Author Closing Comment

ID: 36554450
It was fine. He understood that what I had done was correct and pointed me in the right direction.

Featured Post

Prepare for your VMware VCP6-DCV exam.

Josh Coen and Jason Langer have prepared the latest edition of VCP study guide. Both authors have been working in the IT field for more than a decade, and both hold VMware certifications. This 163-page guide covers all 10 of the exam blueprint sections.

Question has a verified solution.

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

As a database administrator, you may need to audit your table(s) to determine whether the data types are optimal for your real-world data needs.  This Article is intended to be a resource for such a task. Preface The other day, I was involved …
In this blog, we’ll look at how improvements to Percona XtraDB Cluster improved IST performance.
In this video, Percona Solution Engineer Dimitri Vanoverbeke discusses why you want to use at least three nodes in a database cluster. To discuss how Percona Consulting can help with your design and architecture needs for your database and infras…
In this video, Percona Solution Engineer Rick Golba discuss how (and why) you implement high availability in a database environment. To discuss how Percona Consulting can help with your design and architecture needs for your database and infrastr…
Suggested Courses

650 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