Conditional Select in MySQL - mysql

Question

I am working on a mysql query and its giving me headache!
The Scenario:
I am building a website where people can select industries they are interested in (NOTIFY_INDUSTRY). I join the selected values and store in a database field.
Example: a member selects agriculture (id = 9) and oil and gas (id = 13). I join them as 9-13 and store in the database.
Users can select several industries, not limited to two.
Also, members can select an industry (COMPANY_INDUSTRY) it belongs in assuming Information Technology which is stored in the database too.
Sample table (members):
ID
EMAIL
COMPANY_NAME
COMPANY_INDUSTRY
NOTIFY_INDUSTRY
The problem:
When a new user registers on the website, mail (the mails are sent on daily basis) is sent to existing users who have the new user's industry (COMPANY_INDUSTRY) as one of their interested industries (NOTIFY_INDUSTRY).
What i have done:
$sql="select id, email
from members
where notify_industry in (
select company_industry
from members
where datediff($today, date_activated) <= 1)"
This does not select the right members and i do not know the right way to go about it
EDIT - Exact Problem with current output:
Does not return any row, even when it should.
Assuming the new user's company_industry is 9, and there is an existing user with notify_industry: 10-9-20; it is meant to return the existing members email as the new member is in the existing member's categories of interest; but i get blanks

Answer 1

As #Shiplu pointed out, this is largely a normalization issue. Despite what some people seem to think, multi-value columns are murder to try to get right.
Your basic issue is:
You have members, who are interested in one or more companies/industries, which belong to one or more industries. You table structure should probably start as:
Industry
===============
id -- autoincrement
name -- varchar
Company
==============
id -- autoincrement
name -- varchar
Company_Industry
===============
companyId -- fk reference to Company.id
industryId -- fk reference to Industry.id
Member
===============
id -- autoincrement
name -- varchar
email -- varchar
Member_Interest_Industry
=========================
memberId -- fk reference to Member.id
industryId -- fk reference to Industry.id
Member_Interest_Company
========================
memberId -- fk reference to Member.id
companyId -- fk reference to Company.id
To get all companies a member is interested in (directly, or through an industry), you can then run something like this:
SELECT a.name, a.email, c.name
FROM Member as a
JOIN Member_Interest_Company as b
ON b.memberId = a.id
JOIN Company as c
ON c.id = b.companyId
WHERE a.id = :inputParm
UNION
SELECT a.name, a.email, d.name
FROM Member as a
JOIN Member_Interest_Industry as b
ON b.memberId = a.id
JOIN Company_Industry as c
ON c.industryId = b.industryId
JOIN Company as d
ON d.id = c.companyId
WHERE a.id = :inputParm

Answer 2

You should redesign the tables, as others have suggested.
However, barring that, there is a gross hack you can do:
SET sql_mode = 'ANSI';
SELECT notify_members.id, notify_members.email
FROM members notify_members
INNER JOIN members new_members
WHERE CURRENT_DATE - new_members.date_activated <= 1
AND
new_members.company_industry RLIKE ('[[:<:]](' || REPLACE(notify_members.notify_industry, '-', '|') || ')[[:>:]]');
Yuck. Basically, you turn 9-13 into the MySQL regular expression [[:<:]](9|13)[[:>:]], which matches 9, 13, 13-27-61, etc., but does not match 19-131 and the like. (This supports a compound COMPANY_INDUSTRY field, too.)

Answer 3

Use join SQL syntax rather than a select in style..
You need to join the members table to itself.
Currently:
select id, email
from members where notify_industry in
(select company_industry
from members
where datediff($today, date_activated) <= 1
)
Use this style:
select m1.id, m1.email
from members m1
inner join members m2 on m1.company_industry = m.notify_industry
where datediff($today, m2.date_activated) <= 1
Note the use of aliasing to m1 and m2 to help understand which id and emails are returned.

Answer 4

This may get a little ugly but you could try the following
WARNING This will make a Cartesian Product worthy of any Mad Scientist
SELECT NotifyIndustry.id,NotifyIndustry.email
FROM
(
SELECT CONCAT('-',COMPANY_INDUSTRY,'-') company FROM members
WHERE datediff($today, date_activated) <= 1)"
) CompanyIndustry
INNER JOIN
(
SELECT CONCAT('-', NOTIFY_INDUSTRY,'-') who_to_notify
FROM members
) NotifyIndustry
ON LOCATE(company,who_to_notify)>0;

Answer 5

probably not the fastest query ever but this should do the job:
select m_to_notify.id, m_to_notify.email
from members m_to_notify
join members m_new_member
on '-' || m_to_notify.notify_industry || '-'
like '%-' || m_new_member.company_industry || '-%'
where datediff($today, m_new_memberdate_activated) <= 1)