I have two mysql tables as follows:
contacts
---------------
id | name | email
---------------
1 | Jack | jack#test.com
2 | John | john#test.com
3 | Liz | liz#test.com
5 | Jack | jack#test.com
6 | Liz | liz#test.com
7 | Mike | mike#test.com
8 | Jack | jack#test.com
purchases
-------------------
id | contact_id | paid
-------------------
1 | 3 | true
2 | 5 | true
I need unique contact_ids that made purchase and other unique contact_ids that don't have made purchases.
So the final result will be as:
-------------------
id | name | email
------------------
2 | John | john#test.com
3 | Liz | liz#test.com
5 | Jack | jack#test.com
7 | Mike | mike#test.com
I tried the query as:
SELECT * FROM contacts LEFT JOIN purchases ON contacts.id = purchases.user_id
But this is not giving me unique rows as required. I tried several combination of DISTINCT, but I am not getting the result as required.
did you try this?
SELECT COALESCE(purchases.contact_id, contacts.id) as id, name, email
FROM contacts
LEFT JOIN purchases ON contacts.id = purchases.user_id
GROUP BY name
SQL FIDDLE
Something like that should work, but its performance is "?".
SELECT * FROM contacts WHERE id IN (
SELECT DISTINCT id as i FROM purchases
UNION
SELECT DISTINCT contact_id as i FROM purchases
)
GROUP BY id
Related
I have this 2 tables
1st Table "Users"
+----+-----------+----------+
| ID | FirstName | LastName |
+----+-----------+----------+
| 1 | Jeff | Bezos |
| 2 | Bill | Gates |
| 3 | Elon | Musk |
+----+-----------+----------+
2nd Table "Records"
+----+--------+------------+
| ID | IDUser | RecordDate |
+----+--------+------------+
| 1 | 1 | 15/06/2021 |
| 2 | 2 | 05/06/2021 |
| 3 | 2 | 12/06/2021 |
| 4 | 2 | 02/06/2021 |
| 5 | 1 | 17/06/2021 |
+----+--------+------------+
So this 2 tables are linked each other by using a Foreing key Records.IDUsers -> Users.ID
I wanted to make a query that does this
+-----------+----------+----------------+--------------------+
| FirstName | LastName | Lastest Record | Numbers of Records |
+-----------+----------+----------------+--------------------+
| Jeff | Bezos | 17/06/2021 | 2 |
| Bill | Gates | 12/06/2021 | 3 |
| Elon | Musk | NULL | NULL |
+-----------+----------+----------------+--------------------+
You need to use LEFT JOIN in order to get back users without records too; then the MAX and COUNT aggregate functions.
First version: This will return 0 for the number of records instead of NULL, when there are no records for a specific user. Latest record will be NULL as expected.
SELECT
FirstName,
LastName,
MAX(RecordDate) AS LatestRecord,
COUNT(Records.ID) AS NumberOfRecords
FROM Users LEFT JOIN Records on Users.ID = Records.IDUser
GROUP BY Users.ID;
If you want NULL instead of 0 (which normally you do not want), you can use the IF function like this:
SELECT
FirstName,
LastName,
MAX(RecordDate) AS LatestRecord,
IF(COUNT(Records.ID) > 0, COUNT(Records.ID), NULL) AS NumberOfRecords
FROM Users LEFT JOIN Records on Users.ID = Records.IDUser
GROUP BY Users.ID;
Second version: It might happen that running the above query will return an error, something like:
Error: ER_WRONG_FIELD_WITH_GROUP: ...; this is incompatible with sql_mode=only_full_group_by
This happens when/if the ONLY_FULL_GROUP_BY SQL mode is enabled (which it is by default since MySQL 5.7.5). In order to get around this error, you can use the ANY_VALUE function to select the nonaggregated fields:
SELECT
ANY_VALUE(FirstName) AS FirstName,
ANY_VALUE(LastName) AS LastName,
MAX(RecordDate) AS LatestRecord,
COUNT(Records.ID) AS NumberOfRecords
FROM Users LEFT JOIN Records on Users.ID = Records.IDUser
GROUP BY Users.ID;
left join select all user even if does not have records
select * from users left join records on records.IDUser = ID;
I have a table of students with temporary test values like this:
Table students
+----+-------------+-------+-----------+
| id | section_id | age | name |
+----+-------------+-------+-----------+
| 1 | 1 | 18 | Justin |
+----+-------------+-------+-----------+
| 2 | 2 | 14 | Jillian |
+----+-------------+-------+-----------+
| 3 | 2 | 16 | Cherry |
+----+-------------+-------+-----------+
| 4 | 3 | 19 | Ronald |
+----+-------------+-------+-----------+
| 5 | 3 | 21 | Marie |
+----+-------------+-------+-----------+
| 6 | 3 | 21 | Arthur |
+----+-------------+-------+-----------+
I want to query the table such that I want to get all the maximum ages of each section. However, if two students have the same age, the table produced will return the student with smallest id.
Return:
+----+------------+-----+--------+
| id | section_id | age | name |
+----+------------+-----+--------+
| 1 | 1 | 18 | Justin |
+----+------------+-----+--------+
| 3 | 2 | 16 | Cherry |
+----+------------+-----+--------+
| 5 | 3 | 21 | Marie |
+----+------------+-----+--------+
I tried this query:
SELECT ANY_VALUE(id), ANY_VALUE(section_id), MAX(age), ANY_VALUE(name) FROM
(SELECT id, section_id, age, name FROM students ORDER BY id) as X
GROUP BY section_id
Unfortunately, there are instances that id does not match the age and name.
I have on my end:
sql_mode = only_full_group_by
and I don't have a privilege to edit that, hence the any_value function but I have no idea how to use it.
This will do what you want.
It starts by finding the maximum age per section (including duplicates).
Then it joins those results with the minimum id per section (to eliminate duplicates).
And finally, select all fields for the matching id and section combinations.
SELECT s3.*
FROM students s3
INNER JOIN (
SELECT MIN(s2.id) AS id, s2.section_id
FROM students s2
INNER JOIN (
SELECT s1.section_id, MAX(s1.age) AS age
FROM students s1
GROUP BY s1.section_id
) s1 USING (section_id, age)
GROUP BY s2.section_id
) s2 USING (id, section_id);
Working SQL fiddle: https://www.db-fiddle.com/f/aezgAYM6A5KnXykceB7At1/0
I would simply use a correlated subquery:
select s.*
from students s
where s.id = (select s2.id
from students s2
where s2.section_id = s.section_id
order by s2.age desc, s2.id asc
limit 1
);
This is pretty much the simplest way to express the logic. And with an index on students(section, age, id), it should be the most performant as well.
I have two tables in my MySQL database.
The first one stores a list of users, and the other, stores a list of contacts for each user.
Users table:
+----+----------+--------------+
| id | name | phoneNumber |
+----+----------+--------------+
| 1 | David | 661-618-5436 |
| 2 | Sarah | 818-526-4830 |
| 3 | Suzan | 323-623-3493 |
+----+----------+--------------+
Contacts table:
+----+-----------------+--------+--------------+
| id | belongsToUserId | name | phoneNumber |
+----+-----------------+--------+--------------+
| 1 | 1 | Gerard | +18185329384 |
| 2 | 1 | Austin | +18739283847 |
| 3 | 2 | Jamie | +15655468907 |
| 4 | 2 | Jade | +19893828192 |
| 5 | 3 | Phil | +18786754234 |
| 6 | 3 | Duke | +18765467832 |
| 7 | 3 | Gerard | +18185329384 |
| 8 | 3 | Jade | +19893828192 |
+----+-----------------+--------+--------------+
What I want to do, is create a query that efficiently takes 2 user IDs and returns the common contacts by phoneNumber for these two users.
For example: User IDs 1 & 3 both have Gerard | +18185329384 in their contacts so the query will return only him.
What could be the most efficient query for this kind of task?
Thanks :)
If I understood your question correctly, I think this might be what you're looking for:
SELECT
c1.id,
c1.belongsToUserId,
c1.phoneNumber,
c1.name
FROM
Contacts c1
JOIN
Contacts c2 ON (c1.phoneNumber=c2.phoneNumber AND c2.userId=3)
WHERE
c1.belongsToUserId =1
You want a self-join:
select c1.name, c1.phonenumber
from contacts c1 join
contacts c2
on c1.name = c2.name and c1.phonenumber = c2.phonenumber and
c1.belongsToUserId = 1 and
c2.belongsToUserId = 3;
The following SELECT will give you all contacts who has more than 1 User.
SELECT Contacts.name, Contacts.phoneNumber
FROM Users INNER JOIN Contacts ON (Users.id = Contacts.belongsToUserId)
GROUP BY Contacts.name, Contacts.phoneNumber
HAVING COUNT (*) > 1
Following query will display shared contact along with the UseID who's having common contacts.
If you just want to show details of shared contacts, then you can skip first 2 columns.
select min(belongsToUserId) as User1,
max(belongsToUserId) as User2,
name,
phone Number
from contacts
group by name,phoneNumber
having count(*) > 1;
SELECT
cp.name,
cs.phoneNumber
FROM
Contacts cp
INNER JOIN Contacts cs ON
cp.name = cs.name AND cp.phoneNumber = cs.phoneNumber
AND
cp.belongsToUserId IN ( 1,3 );
I have two tables messages and users I want to find out which users received the messages however the query is only returning one message.
My Schemas are as follow
Messages
msg_id | msg_content | recipients |
-----------------------------------
1 | Hello world | 1,2,3,4,5
2 | Test | 1,3,5
3 | Welcome | 1,2,4
Users
uid | fname | lname |
---------------------------
1 | John |Doe |
2 | Jane |Doe |
3 | Mark |Someone |
4 | Mary |lady |
5 | Anthony |Doe |
So I would love to see my results simply as
msg_id | msg_content | recipients |
-----------------------------------
1 | Hello world | John,Jane,Mark,Mary,Anthony
2 | Test | John,Mark,Anthony
3 | Welcome | John,Jane,Mary
So I am doing my query as so
SELECT msg_id,msg_content,fname AS recepients FROM messages a
LEFT JOIN users ON uid IN(a.recipients)
When I run that query I only get one recipient. Please advice. Thanks.
I think you have to use a alternative way for create tables
Messages
msg_id | msg_content |
----------------------
1 | Hello world |
2 | Test |
3 | Welcome |
Users
uid | fname | lname |
---------------------------
1 | John |Doe |
2 | Jane |Doe |
3 | Mark |Someone |
4 | Mary |lady |
5 | Anthony |Doe |
users_has_messages
uhm_id | uid | msg_id |
---------------------------
1 | 1 | 1 |
2 | 2 | 1 |
3 | 3 | 1 |
4 | 2 | 2 |
5 | 1 | 3 |
Then you can use your code
Okay, so this schema isn't the best (using comma separated lists of IDs is not a great idea, and the performance of any joins will get pretty bad pretty quick). Best bet is to have a third table mapping uid's to msg_id's as mentioned by #Thilina.
That said, this query will do probably what you're after:
SELECT msg_id,msg_content,GROUP_CONCAT(fname) AS recepients FROM messages a
LEFT JOIN users ON FIND_IN_SET(uid, a.recipients)
GROUP BY msg_id
I tried this in Oracle 12c and it is working fine.
So basically what I did is
- Separate the userid from recipient field and used this a columns.
- Join with USERS table to get user fnames
- Used LISTAGG function to aggregate it back.
For MySql we need to find the corresponding functions to Separate the IDs between commas, Convert it to rows and Aggregate. But the inherent logic would be same.
with users (user_id,fname) as (
select 1 ,'John' from dual union
select 2 ,'Jane' from dual union
select 3 ,'Mark' from dual union
select 4 ,'Mary' from dual union
select 5 ,'Anthony' from dual
),
messages(msg_id, msg_content,recipients) as(
select 1,'Hello world','1,2,3,4,5' from dual union
select 2 , 'Test' ,'1,3,5' from dual union
select 3,' Welcome','1,2,4' from dual
),
flat as(
select msg_id,msg_content,
REGEXP_SUBSTR (recipients, '[^,]+', 1, COLUMN_VALUE) as user_id
from messages,
TABLE(
CAST(
MULTISET(
SELECT LEVEL
FROM DUAL
CONNECT BY LEVEL <= REGEXP_COUNT(recipients ,',' ) + 1
) AS SYS.ODCINUMBERLIST
)
)
),
unames as
( select f.msg_id,f.msg_content,u.fname from flat f inner join users u
on f.user_id = u.user_id
order by f.msg_id
)
SELECT msg_id,msg_content,LISTAGG(fname, ',') WITHIN GROUP (ORDER BY fname) as recipients
from unames
group by msg_id,msg_content
I have the following 3 tables with IDs
Table: users
user | name
1 | Joe
2 | John
Table: user_id1
user | id1
1 | 2
1 | 3
2 | 5
Table: user_id2
user | id2
1 | 3
1 | 4
I would like to get the following result for each user
name | ids 1 | ids 2
Joe | 2,3 | 3,4
John| 5 | NULL
I use this query:
SELECT
user.name,
GROUP_CONCAT(user_id1.id1) AS "ids1",
GROUP_CONCAT(user_id2.id2) AS "ids2"
FROM users
LEFT JOIN user_id1
ON user_id1.user=users.user
LEFT JOIN user_id2
ON user_id2.user=users.user
But I get this result:
name | ids1 | ids2
Joe | 2,2,3,3 | 3,4,3,4
John | 5 | NULL
What is wrong?
Thanks for your help
Using DISTINCT should solve it
SELECT
user.name,
GROUP_CONCAT(DISTINCT user_id1.id1) AS "ids1",
GROUP_CONCAT(DISTINCT user_id2.id2) AS "ids2"
FROM users
LEFT JOIN user_id1
ON user_id1.user=users.user
LEFT JOIN user_id2
ON user_id2.user=users.user