Solved

Updating fields in one table via querying another table

Posted on 2011-02-13
3
307 Views
Last Modified: 2012-05-11
hi guys i am trying to populate how many products are available within a certain category in Mysql database but i am unsure of the sql query to run. the 2 table examples are below.

Table 1 with fields id/category/product. field "id" is an auto increment field and can be ignored.
the layout is referenced below
1/1/1
2/1/2
3/1/3
4/1/4
5/4/5

i need to somehow get a total amount of products that are within each category i.e in the example above there would be a total products of 4 and they are within category 1 and 1 item within category 4


Table 2 has fields named id/category/product. the category names only appear once so go from 1 to 20 for example but i must update the field within this table named "product" and put the amount of products found within table 1 into each category
1/pens/0
2/rulers/0
3/mats/0
4/inks/0

So if the query ran i would expect an update of field "product" in table 2 to then change to the below
1/pens/4
2/rules/0
3/mats/0
4/inks/1

hope this is easy enough to follow and thank you in advance for your help
0
Comment
Question by:TG-Steve
[X]
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
  • 2
3 Comments
 
LVL 60

Expert Comment

by:Kevin Cross
ID: 34883271
TG-Steve,

Yes, you can use an update with a join like so in MySQL:

UPDATE Table2 t2, (SELECT category, COUNT(product) `cnt` FROM Table1) t1
SET t2.product = t1.cnt
WHERE t2.category = t1.category
;

Open in new window


Regards,
Kevin
0
 
LVL 60

Accepted Solution

by:
Kevin Cross earned 250 total points
ID: 34883273
Sorry, forgot the GROUP BY:
UPDATE Table2 t2, (SELECT category, COUNT(product) `cnt` FROM Table1 GROUP BY category) t1
SET t2.product = t1.cnt
WHERE t2.category = t1.category
;

Open in new window

0
 

Author Closing Comment

by:TG-Steve
ID: 34925656
Tested today and works perfect thankyou
0

Featured Post

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.

Question has a verified solution.

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

Suggested Solutions

Containers like Docker and Rocket are getting more popular every day. In my conversations with customers, they consistently ask what containers are and how they can use them in their environment. If you’re as curious as most people, read on. . .
In this series, we will discuss common questions received as a database Solutions Engineer at Percona. In this role, we speak with a wide array of MySQL and MongoDB users responsible for both extremely large and complex environments to smaller singl…
Nobody understands Phishing better than an anti-spam company. That’s why we are providing Phishing Awareness Training to our customers. According to a report by Verizon, only 3% of targeted users report malicious emails to management. With compan…

752 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