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

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.)