How to remove matches between unioned tables with joined tables - mysql

Question

I have 2 Tables
emails and fields
emails is just a list of emails and their unique identifiers and fields is in fifth normal form (i think) with a column of values(that ID data in the second column),a data column, and ids that link to the uuids in the first table.
For example:
Table 1:
ID EMAIL
-- -----
1a2 Test#Test
2a3 email#email|
3a4 add#add
Table 2:
value Data ID
----- ------ ---
1 123 Main 1a2
2 John Smith 1a2
3 US 1a2
4 555-555-5555 1a2
In this case, table 2 only shows the data for "1a2" because they were the only one to fill them out.
So I'm trying to make a table, that couples email to the corresponding country codes AND also provides the emails that haven't registered country codes as a Null value
I've tried using UNION to display all the emails from Table 1 on Table 2 after joining table 1 and 2 on ID and then using where for the value but that shows all the emails that have the proper country code and then duplicates them in the UNIONed portion as well.
This is an example of what I'm getting:
EMAIL COUNTRY CODE
----- ------------
test#test US
test#test NULL
email#email NULL
add#add NULL
You'll notice that test#test is duplicated due to the union not having the proper filter
My code looks like:
select
e.email as "Email",
f.value as "Country Code"
from
email e
join
fields f
ON e.id = f.id
where
f.value = '3'
[[and f.data like concat({{CountryCode}},'%')]]
-- curly brackets are for user entered variables
Anyways, all said and done. I'm looking for a table that appears something like this with No Duplicates
EMAIL COUNTRY CODE
----- ------------
test#test US
email#email NULL
add#add NULL

Answer 1

You are storing your user metadata in key value format. One approach here is to left join the user table to a subquery which pivots to find the country:
SELECT
e.EMAIL,
f.country_code
FROM email e
LEFT JOIN
(
SELECT ID, MAX(CASE WHEN value = 3 THEN Data END) AS country_code
FROM fields
GROUP BY ID
) f
ON e.ID = f.ID;
Demo

Answer 2

You can try using max() aggregation and group by -
select
e.email as "Email",
max(f.value) as "Country Code"
from
email e
left join
fields f
ON e.id = f.id
where
f.value = '3'
[[and f.data like concat({{CountryCode}},'%')]]
group by e.email

Answer 3

You can make the field you're interested in part of your LEFT JOIN condition.
SELECT
e.EMAIL,
f.data as countryCode
FROM email e
LEFT JOIN fields f ON f.value=3 AND e.ID=f.ID
Users with a value for that field will return it. Users without will simply be NULL due to it being a LEFT join.
If you want to do a condition on the fields value, then you'll need to include a check for null as well.
SELECT
e.EMAIL,
f.data as countryCode
FROM email e
LEFT JOIN fields f ON f.value=3 AND e.ID=f.ID
WHERE
f.data IS NULL
OR f.data='US'

Answer 4

Well I feel pretty silly after posting this, but I found the solution and am going to post it in case someone else bumps into the issue.
left join
fields f
ON e.id = f.id
where
f.value = '3' OR f.value is null
[[and f.data like concat({{CountryCode}},'%')]]
I just needed to add an "OR" for null values. Sorry if I wasted anyone's time, I was clearly overcomplicating things and managed to achieve what I was trying to do without a union at all.