Let's say that I have two tables A and B where
A is table countries with columns id, name, created, modified
that contains a bunch of countries
And B is table users with columns id, first_name, last_name, email, country_id, created, modified
that contains a bunch of users linked to countries via foreign key country_id
What is the most efficient query to get all the countries that don't have a user with email address "myemail#test.com" associated to it?
I tried something like the following but that didn't work:
SELECT DISTINCT
c.*
FROM
countries c
LEFT JOIN
users u ON u.country_id = c.id
WHERE
u.email <> 'myemail#test.com'
Thanks for any help
NOTE I also tried putting the condition on the email column in the ON clause that didn't work either
A left join is fine, you just need to set it up correctly:
SELECT c.*
FROM countries c LEFT JOIN
users u
ON u.country_id = c.id AND u.email = 'myemail#test.com'
WHERE u.country_id IS NULL;
In terms of performance, this should be pretty similar to NOT EXISTS and NOT IN (although I do not recommend the latter because it has different behavior when there are NULL values).
When you say "that don't have a user with email address "myemail#test.com"",
do you mean no email address -or- not that exact email address?
Updated
Then this should do:
SELECT DISTINCT c.*
FROM countries c
LEFT JOIN users u ON u.country_id = c.id and u.email = 'myemail#test.com'
WHERE u.country_id is null
Which I believe is what Gordon already had.
Updated Again
In that case, try:
SELECT DISTINCT c.*
FROM countries c
INNER JOIN users u ON u.country_id = c.id and ISNULL(u.email, '') = ''
This looks for Null or Empty String email adresses all others are excluded from the join and therefore from the result set.
I hope this helps.
Related
Table 1 :- tbl_contacts
Fields
user_id
contact_id
first_name
last_name
Table 2 :- tbl_phone_details
Fields
contact_id
phone_number
phone_type
Table 3 :- tbl_email_details
Fields
contact_id
email_address
email_type
QUERY -
SELECT
tbl_contacts.*, tbl_email_details.*, tbl_phone_details.*
FROM
tbl_contacts, tbl_email_details,
tbl_phone_details
WHERE
tbl_contacts.user_id = '1'
I want to get first_name, last_name, Phone and Email details of particular user_id. I have used above query but its giving me repeated results and I am having less knowledge on DB queries like JOIN and INNER QUERY.
If anyone has any idea, please kindly help.
OUTPUT NEEDED:-
contact_id, first_name, last_name, phone_number, phone_type, email_address, email_type
(Here email and phone number can have 1 or more values for particular users).
Try like this
If you want to retrieve data for particular ID
SELECT T.contact_id,
T.first_name,
T.last_name,
P.phone_number,
P.phone_type,
E.email_address,
E.email_type
FROM tbl_contacts T LEFT JOIN tbl_phone_details P ON
T.contact_id = P.contact_id
LEFT JOIN tbl_email_details E ON
T.contact_id = E.contact_id
WHERE T.contact_id = #contact_id
If you want to retrieve all data
SELECT T.contact_id,
T.first_name,
T.last_name,
P.phone_number,
P.phone_type,
E.email_address,
E.email_type
FROM tbl_contacts T LEFT JOIN tbl_phone_details P ON
T.contact_id = P.contact_id
LEFT JOIN tbl_email_details E ON
T.contact_id = E.contact_id
SELECT tbl_contacts.*, tbl_email_details.*, tbl_phone_details.* FROM
tbl_contacts, tbl_email_details, tbl_phone_details WHERE
tbl_contacts.user_id = '1'
You forgot to mention the condition by which you are going to join all the tables!
SELECT c.first_name, c.last_name, p.phone_number, e.email_address
FROM tbl_contacts c, tbl_email_details e, tbl_phone_details p
WHERE tbl_contacts.user_id = '1'
AND c.contact_id = e.contact_id
AND e.contact_id = p.contact_id;
SELECT c.contact_id, c.first_name, c.last_name,
phone.phone_number, phone.phone_type,
email.email_address, email.email_type
FROM tbl_contacts c
LEFT JOIN tbl_email_details email ON c.contact_id = email.contact_id
LEFT JOIN tbl_phone_details phone ON c.contact_id = phone.contact_id
WHERE tbl_contacts.user_id = '1'
Sql queries are easy to learn and write and they are very useful in getting the important data from database. Joins are used to basically fetch the data from two or more tables on the bases of common column in both tables.
Inner Join will select those values that are common in both of the tables.
Left Join will select all the data from the left table and Right Join will select all the data from right table on the basis of id.
These are the basics of SQL and you must know how to fetch accurate data using them.
this is how I would make that request with JOIN ... but there might be some better or faster way to do it.
SELECT first_name, last_name, phone_number, email_address
FROM tbl_contacts
JOIN tbl_phone_details
ON tbl_contacts.contact_id=tbl_phone_details.contact_id
JOIN tbl_email_details
ON tbl_email_details.contact_id=tbl_contacts.contact_id
WHERE tbl_contacts.user_id = '1';
And just so you don't get lost in all the different answers here (which are probably all correct):
you don't need to give an aliase name to your tables (it's just for readability)
you don't need to mention the table names in your column list if the column name is unique (e.g first_name is only in tbl_contacts). Just if you want the contact_id then you should decide which one (e.g. tbl_phone_details.contact_id)
the multi-select as Jayaram proposed, is exactly the same as the JOIN. MySQL handles both queries the same way (I just didn't see his answer when I responded, sorry)
So, the two tables in question:
userinfo: id(PK), users_id(FK to users table), name, surname
doctorpatient: id(PK), doctor_id(FK to users table), patient_id(FK to users table)
The idea is each doctor is assigned a few patients via the doctorpatient table. What I want to do is return an array of arrays, where each of the inner arrays contains this:
users_id(doctor), name(doctor), surname(doctor), users_id(patient), name(patient), surname(patient)
Can this even be done using purely SQL? I tried this:
SELECT userinfo.users_id,
userinfo.name,
userinfo.surname,
u2.users_id,
u2.name,
u2.surname
FROM doctorpatient
RIGHT OUTER JOIN userinfo
ON doctorpatient.doctor_id = userinfo.users_id
LEFT OUTER JOIN userinfo AS u2
ON doctorpatient.patient_id = u2.users_id
but no matter what combination of joins I try, it never comes out right. I tried getting the data in three separate queries and then somehow get the result I need using PHP, but I got nowhere with that.
Edit: What I want is this:
array(
subarray1(patient_id1,
patient_name1,
patient_surname1,
doctor_id1,
doctor_name1,
doctor_surname1)
subarray2(patient_id2,
patient_name2,
patient_surname2,
doctor_id1,
doctor_name1,
doctor_surname1)
etc...
where one doctor can have multiple patients. What my query gets me looks something like this:
array(
subarray1(patient_id1,
patient_name1,
patient_surname1,
)
subarray2(patient_id2,
patient_name2,
patient_surname2,
)
etc...
But most of the data is null.
I think a simple JOIN may be sufficient. The OUTER JOINs appear to be causing the null values because it tries to treat the doctors as patients.
SELECT u1.users_id AS doctor_id,
u1.name AS doctor_name,
u1.surname AS doctor_surname,
u2.users_id AS patient_id,
u2.name AS patient_name,
u2.surname AS patient_surname
FROM doctorpatient AS d JOIN userinfo AS u1 ON d.doctor_id = u1.users_id
JOIN userinfo AS u2 ON d.patient_id = u2.users_id
Try this:
SELECT
u.id as user_id,
u.name as user_name
u.surname as user_usrname
d.id as doc_id,
d.name as doc_name,
d.surname as doc_surname
FROM doctorpatient as dp
LEFT JOIN userinfo as u ON (dp.pacient_id = u.id)
LEFT JOIN userinfo as d ON (dp.doctor_id = d.id)
I'm trying to write an SQL statement to retrieve a list of users from a database, along side their company name (if they have a company associated with them). However, there are a couple gotchas:
Not all users have companies, but I still need to show these people in the list.
Even if a user has a company, that company could be soft-deleted (the record is still in the database, but is flagged with is_deleted = 1), and I don't want to show users that are associated with "deleted" companies.
So essentially I want to SELECT from the User table and LEFT JOIN the company table, but I don't want to include the User record at all if the company they are assigned to is_deleted.
My first inclination is that I would have to use a UNION to merge two queries together, but I was hoping there would be a cleaner way to do it?
Using Mysql 5.1
SELECT U.name Username, C.name Company
FROM User U
LEFT OUTER JOIN Company C
ON U.companyid = C.id
WHERE C.id IS NULL OR C.is_deleted = 0
C.id IS NULL gets the users with no company, and C.is_deleted = 0 gets the users with companies that haven't been soft-deleted.
Try joining to a table that excludes the deleted companies:
SELECT U.Name, C.Name
FROM User U LEFT OUTER JOIN
(SELECT CompanyId, CompanyName
FROM Company
WHERE is_deleted = 0)
C ON U.CompanyId = C.CompanyId
I have a table for referred users (contains an email address and date columns) and a table for users.
I run to get the top referers:
SELECT count(r.Email) as count, r.Email
FROM refs r
WHERE r.referredOn > '2011-12-13'
GROUP BY email
ORDER BY count DESC
But I want to join this with the users table so it displays with other data in the user table, I thought a join would work. Left join becuase emails may be entered incorrectly, some people put first name etc under refs.Email
SELECT count(r.Email) as count, r.Email, u.*
FROM refs r LEFT JOIN users u ON u.email_primary = r.Email
WHERE r.referredOn > '2011-12-13'
GROUP BY email
ORDER BY count DESC
With the above query the count is incorrect, but I don't know why.
Try this one:
SELECT count(r.Email) as count, r.Email
FROM refs r
INNER JOIN users u ON u.email_primary = r.Email
WHERE r.referredOn > '2011-12-13'
GROUP BY email
ORDER BY count DESC
if your adding new column from users u you also need to add it on your group by clause.
Regards
Unfortunately, a LEFT JOIN wont help you here; what this type of join says is give me all the rows in users that match my email, as well as all the rows that have no match on email. If the email doesn't match, then they wont come back as you want.
So you can't use a the left join condition here the way you want.
If you enforced the fact that they had to enter an email everytime, and it was a valid email etc, then you could use an INNER JOIN.
JOINs are usually used to follow referential integrity. So, for example, I have a user with an id in one table, and another table with the column userid - there is a strong relationship between the two tables I can join on.
Jeft Atwood has a good explantion of how joins work.
SEE if this will help you:
SELECT e.count, e.email, u.col1, u.col2 -- etc
FROM (
SELECT count(r.Email) as count, r.Email
FROM refs r
WHERE r.referredOn > '2011-12-13'
GROUP BY email
) e
INNER JOIN
users u ON u.email_primary = e.Email
Instead of a direct join, you could TRY to use your counting query as a subquery-table type..
I wrote this query
SELECT *, count(r.Email) as count FROM refs r
LEFT OUTER JOIN users u ON r.email = u.email_primary
WHERE u.uid IS NOT NULL
GROUP BY u.uid
ORDER BY count DESC
Which showed me that the reason the count was wrong was because some of the email addresses are used twice in the users table (users sharing 'family' email address), this doubled my count, the above query shows each separate user account.
i have a MySQL SELECT query which fetches data from 6 tables using Mysql JOIN. here is the MySQL query i am using.
SELECT
u.id,u.password,
u.registerDate,
u.lastVisitDate,
u.lastVisitIp,
u.activationString,
u.active,
u.block,
u.gender,
u.contact_id,
c.name,
c.email,
c.pPhone,
c.sPhone,
c.area_id,
a.name as areaName,
a.city_id,
ct.name as cityName,
ct.state_id,
s.name as stateName,
s.country_id,
cn.name as countryName
FROM users u
LEFT JOIN contacts c ON (u.contact_id = c.id)
LEFT JOIN areas a ON (c.area_id = a.id)
LEFT JOIN cities ct ON (a.city_id = ct.id)
LEFT JOIN states s ON (ct.state_id = s.id)
LEFT JOIN countries cn ON (s.country_id = c.id)
although query works perfectly fine it sometimes returns duplicate results if it finds any duplicate values when using LEFT JOIN. for example in contacts table there exist two rows with area id '2' which results in returning another duplicated row. how do i make a query to select only the required result without any duplicate row. is there any different type of MySQL Join i should be using?
thank you
UPDATE :
here is the contacts table, the column area_id may have several duplicate values.
ANSWER :
there was an error in my condition in last LEFT JOIN where i have used (s.country_id = c.id) instead it should be (s.country_id = cn.id) after splitting the query and testing individually i got to track the error. thank you for your response. it works perfectly fine now.
Duplicating the rows like you mentioned seems to indicate a data problem.
If users is your most granular table this shouldn't happen.
I'd guess, then, that it's possible for a single user to have multiple entries in contacts
You could use DISTINCT as mentioned by #dxprog but I think that GROUP BY is more appropriate here. GROUP BY whichever datapoint could potentially be duplicated....
After all, if a user has corresponding contact records, which one are you intending to JOIN to?
You must specify this if you want to remove "duplicates" because, as far as the RDBMS is concerned, the two rows matching
LEFT JOIN contacts c ON (u.contact_id = c.id)
Are, in fact, distinct already
I think a DISTINCT may be what you're looking for:
SELECT DISTINCT
u.id,u.password,
u.registerDate,
u.lastVisitDate,
u.lastVisitIp,
u.activationString,
u.active,
u.block,
u.gender,
u.contact_id,
c.name,
c.email,
c.pPhone,
c.sPhone,
c.area_id,
a.name as areaName,
a.city_id,
ct.name as cityName,
ct.state_id,
s.name as stateName,
s.country_id,
cn.name as countryName
FROM users u
LEFT JOIN contacts c ON (u.contact_id = c.id)
LEFT JOIN areas a ON (c.area_id = a.id)
LEFT JOIN cities ct ON (a.city_id = ct.id)
LEFT JOIN states s ON (ct.state_id = s.id)
LEFT JOIN countries cn ON (s.country_id = c.id)
This should only return rows where the user ID is distinct, though you may not get all the joined data you'd hoped for.