Trouble with my SQL JOIN statement after using WHERE IN - mysql

Question

SELECT contactid, firstname, email, phone
FROM vtiger_contactscf t1
WHERE email
IN (SELECT email FROM vtiger_contactscf WHERE CHAR_LENGTH(email)>0 GROUP BY email HAVING count(*)>1)
OR phone
IN (SELECT phone FROM vtiger_contactscf WHERE CHAR_LENGTH(phone)>0 GROUP BY phone HAVING count(*)>1)
The above SQL query produces a table with all of the contacts i have which have the same email or phone number as another contact.
For each contact I get the contactid, firstname, phone, and email. However, I also want to JOIN the lastname. But lastname data is stored in a different table. That table also has contactid so i could use it for the JOIN ON. But when I simply add a JOIN t2 ON t1.contactid=t2.contactid it still doesn't work.
Full code with the join statement:
SELECT t1.contactid, t1.firstname, t2.lastname t1.email, t1.phone
FROM vtiger_contactscf t1
WHERE t1.email
IN (SELECT email FROM vtiger_contactscf WHERE CHAR_LENGTH(email)>0 GROUP BY email HAVING count(*)>1)
OR t1.phone
IN (SELECT phone FROM vtiger_contactscf WHERE CHAR_LENGTH(phone)>0 GROUP BY phone HAVING count(*)>1)
JOIN vtiger_contactsdetails t2 ON t1.contactid = t2.contactid
What am I doing wrong?

Answer 1

JOIN is an operator that belongs in the FROM clause:
SELECT c.contactid, c.firstname, cd.lastname c.email, c.phone
FROM vtiger_contactscf c JOIN
vtiger_contactsdetails cd
ON c.contactid = cd.contactid
WHERE c.email IN (SELECT c2.email
FROM vtiger_contactscf c2
WHERE CHAR_LENGTH(c2.email) > 0
GROUP BY c2.email
HAVING count(*) > 1
) OR
c.phone IN (SELECT c2.phone
FROM vtiger_contactscf c2
WHERE CHAR_LENGTH(c2.phone) > 0
GROUP BY phone
HAVING count(*) > 1
);
That said, this seems a little strange. You have two tables with essentially the same primary key? Is it possible that one contactid could have multiple rows in the details table? If so, the above logic may not work, because the multiple records could have the same phone number or email.
You can fix this and simplify the query using EXISTS:
SELECT c.contactid, c.firstname, cd.lastname c.email, c.phone
FROM vtiger_contactscf c JOIN
vtiger_contactsdetails cd
ON c.contactid = cd.contactid
WHERE EXISTS (SELECT 1
FROM vtiger_contactscf c2
WHERE CHAR_LENGTH(c2.email) > 0 AND c2.email = c.email AND c2.contactid <> c.contactid
) OR
EXISTS (SELECT c2.phone
FROM vtiger_contactscf c2
WHERE CHAR_LENGTH(c2.phone) > 0 AND c2.phone = c.phone AND c2.contactid <> c.contactid
);
This may not look much simpler, but EXISTS can take advantage of an index on vtiger_contactscf(phone, contactid) and vtiger_contactscf(email, contactid).