I am trying to get a single row at random from the Sponsor table joined to the Company table. The follow query almost works but will sometimes return a NULL Sponsor.
Can anyone see what I am doing wrong here?
SELECT C.ID AS CompID, C.Name AS CompName, S.ID AS SponID, S.Name AS SponName
FROM Company C
LEFT JOIN Sponsor S ON S.ID = (SELECT ID FROM Sponsor WHERE Company = C.ID ORDER BY RAND() LIMIT 1)
Data Sample:
Company Table
| ID | Name |
| 1 | MyCompany |
Sponsor Table
| ID | Company | Name |
| 1 | 1 | Bruce |
| 2 | 1 | John |
Query Results in one of the following:
| CompID | CompName | SponsID | SponName |
| 1 | MyCompany | 1 | Bruce |
| CompID | CompName | SponsID | SponName |
| 1 | MyCompany | 2 | John |
| CompID | CompName | SponsID | SponName |
| 1 | MyCompany | NULL | NULL |
Because of RAND() your subquery is not deterministic and thus is executed for every row in Sponsor table and every time retuns a random ID which might match or not the ID of the current row. So it's not only possible, that no row will match the random ID. It's also possible that multiple rows will.
For the sample data with two sponsors the subquery may return folowing values:
(1, 1) will match the first row (1=1, 2=1)
(1, 2) will match both rows (1=1, 2=2)
(2, 1) will match no row (1=2, 2=1)
(2, 2) will match the second row (1=2, 2=2)
To guarantee that the subquery is executed only once, you can use it the SELECT clause. Then join the result as derived table with the Sponsor table:
SELECT C.*, S.Name AS SponName
FROM (
SELECT C.ID AS CompID, C.Name AS CompName, (
SELECT ID FROM Sponsor WHERE Company = C.ID ORDER BY RAND() LIMIT 1
) as SponID
FROM Company C
) C
LEFT JOIN Sponsor S ON S.ID = C.SponID
Demo: http://rextester.com/LSSJT25902
Related
I'm trying to look if a record of a table, has at least one record on a pivot table that is used on a many to many relationship.
The table Attendant is:
| ID | NAME |
|----|--------|
| 1 | Name A |
| 2 | Name B |
| 3 | Name C |
And the Attendant_Event pivot table has the following structure
| ID | attendant_id | event_id | uuid |
|----|----------------|------------|--------|
| 1 | 1 | 1 | xxx |
| 2 | 1 | 2 | yyy |
| 3 | 3 | 1 | zzz |
| 4 | 3 | 2 | www |
| 5 | 1 | 3 | xyx |
| 6 | 3 | 3 | rer |
My query is trying to count the attendants that has a least one record on the pivot table, but count all the records as one.
For example, the expected result will be a table like this:
| STATUS | COUNT |
|--------|--------|
| YES | 2 |
| NO | 1 |
This results are expected because:
Only the Attendants with ID 1 and 3 has a record on the Attendant_Event table. This told us that the number of Attendants with rows on the pivot table is 2.
The Attendant with ID 2 has no records, so the number of attendants with no records on the pivot table is 1.
By now, my query is the following:
SELECT IF(uuid <=> NULL, 'NO', 'YES') as status, count(*) as count FROM attendants att LEFT JOIN attendant_event ae ON ae.attendant_id = att.id GROUP BY status
But this is showing me a result like this.
| STATUS | COUNT |
|--------|--------|
| YES | 6 |
| NO | 1 |
This means that, count each of the rows. If we take the previous example, both Attendants with id 1 and 3 has 3 records on the pivot table. So It gives 6 instead of the two that I'm looking for.
What I'm doing wrong?
You may want to select the attendant IDs with their respective YES/NO first, then count them, something like:
SELECT status, count(distinct attendant_id) as count FROM (
SELECT IF(ae.uuid IS NULL, 'NO', 'YES') as status, ae.attendant_id
FROM attendants att LEFT JOIN attendant_event ae ON ae.attendant_id = att.id
GROUP BY ae.attendant_id) x
GROUP BY status
When you make left join, you create intersection, that is larger than attendants table. Your join consists of rows with repeating attendant_id and different event uuid.
You can watch the intersection by executing SELECT IF(uuid <=> NULL, 'NO', 'YES') as status, att.id, ae.uuid FROM attendants att LEFT JOIN attendant_event ae ON ae.attendant_id = att.id. It includes 7 rows, 6 of them are with YES events for two active attendats and 1 row with NO events.
So you should count only distinct values:
SELECT IF(uuid <=> NULL, 'NO', 'YES') as status, count(distinct(att.id)) as count
FROM attendants att
LEFT JOIN attendant_event ae ON ae.attendant_id = att.id
GROUP BY status
I have a Purchases table, where I'm trying to select all rows where first name, surname and email are duplicates (for all 3).
Purchases table:
| purchase_id | product_id | user_id | firstname | surname | email |
| ------------- | -----------| ------------- | ----------- | --------- | ----------- |
| 1 | 1 | 777 | Sally | Smith | s#gmail.com |
| 2 | 2 | 777 | Sally | Smith | s#gmail.com |
| 3 | 3 | 777 | Sally | Smith | s#gmail.com |
| 4 | 1 | 888 | Bob | Smith | b#gmail.com |
Further to this, each product ID corresponds to a product type in a 'Products' table, and I'm trying to filter by 'lawnmower' purchases (so only product ID 1 & 2)
Products table:
| product_type | product_id |
| ------------- | -----------|
| lawnmower | 1 |
| lawnmower | 2 |
| leafblower | 3 |
I'm hoping to write a query that will return all purchases of the 'lawnmower' type where first name, last name, and email are duplicates (so would return the first two rows of the Purchases table).
This is where my query is at so far, however it's not returning accurate data (e.g. I know I have around 350 duplicates and it's returning 10,000 rows):
SELECT t. *
FROM database_name.purchases t
JOIN (
SELECT firstname, surname, email, count( * ) AS NumDuplicates
FROM database_name.purchases
GROUP BY firstname, surname, email
HAVING NumDuplicates >1
)tsum ON t.firstname = tsum.firstname
AND t.surname = tsum.surname
AND t.email = tsum.email
INNER JOIN database_name.products p2 ON t.product_id = p2.product_id
WHERE p2.product_type = 'lawnmower'
Just wanting to know what I need to tweak in my query syntax.
You know that you should be returning Sally Smith. Create a table from the results of your query above. Then Select * from that table where first_name=sally and surname=Smith. See if you can figure out where you are going wrong based on that. This will help you debug these type of issues yourself in the future.
Your inner SELECT does not filter on the product type. It gets all customers who have purchased any two items. Then you join it to purchases and therefore also get the purchases of customers who have bought any two items and, possibly only one, lawnmower. Add a filter on the product type in the subquery too:
SELECT t.*
FROM database_name.purchases t
INNER JOIN (SELECT purchases.userid
FROM database_name.purchases
INNER JOIN database_name.products
ON products.product_id = purchases.product_id
WHERE products.product_type = 'lawnmower'
GROUP BY userid
HAVING count(*) > 1) s
ON t.user_id = s.user_id
INNER JOIN database_name.products p
ON t.product_id = p.product_id
WHERE p.product_type = 'lawnmower';
Your schema also is problematic -- denormalised. firstname, surname and email depend on user_id (Note that I only grouped and joined using the user_id, that's enough,). So they shouldn't be in purchases, only user_id. product_type better by an ID referencing to some product type table too.
I have a table A that contains tree columns, id, users ids and vehicle id. And a table B that contains vehicleid, and vehicle name.
Table A
---------------------------
| Id | User_id |Vehicle_id|
---------------------------
| 1 | 1 | 2 |
| 2 | 1 | 3 |
| 3 | 1 | 4 |
| 4 | 2 | 2 |
| 5 | 2 | 3 |
| 6 | 4 | 5 |
---------------------------
Table B
-------------------
| Id |Vehicle_name|
-------------------
| 1 | Car |
| 2 | Bike |
| 3 | Plane |
| 4 | Boat |
| 5 | Rocket |
-------------------
Given a user id, I need to get all vehicle names, that doesn't match with table A. I've tried Outer joins, but I can't manage to do get the info that i need.
For example: Given user id 1, the query should return Car and Rocket.
thanks in advance
This is simple enough using not in or not exists:
select b.*
from b
where not exists (select 1
from a
where a.vehicle_id = b.id and a.user_id = #a_user_id
);
I also thought of using a cross join and was able to get the output in case you are more comfortable with join logic.
SELECT CJOIN.USER_ID, CJOIN.VEHICLE_ID, CJOIN.VEHICLE_NAME
FROM
(SELECT DISTINCT A.USER_ID, B.ID AS VEHICLE_ID, B.VEHICLE_NAME FROM TABLE_A A CROSS JOIN TABLE_B B) CJOIN
LEFT JOIN
TABLE_A D
ON CJOIN.USER_ID = D.USER_ID AND CJOIN.VEHICLE_ID = D.VEHICLE_ID
WHERE D.USER_ID IS NULL AND D.VEHICLE_ID IS NULL;
First, I got all possible combinations of USER_ID x VEHICLE_ID by a cross join and used this table in a left join to pull records for which there is no match.
I'm currently writing a ticket system that has three tables
one for users:
users
+----+-----------+----------+
| ID | FirstName | LastName |
+----+-----------+----------+
| 1 | First | User |
| 2 | Second | User |
| 3 | Third | User |
| 4 | Fourth | User |
| 5 | Fifth | User |
+----+-----------+----------+
one for tickets:
ticket
+----+---------------+
| ID | TicketSubject |
+----+---------------+
| 1 | Ticket #1 |
| 2 | Ticket #2 |
| 3 | Ticket #3 |
| 4 | Ticket #4 |
+----+---------------+
and one to assign users to tickets to action (can be more than one user per ticket):
ticket_assigned
+----+----------+--------+
| ID | TicketID | UserID |
+----+----------+--------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 2 | 1 |
| 4 | 3 | 5 |
| 5 | 3 | 3 |
+----+----------+--------+
I'm trying to create a summary to show each user, and how many tickets they have assigned to them, example:
+------------+-------+
| Name | Count |
+------------+-------+
| First | 2 |
| Second | 1 |
| Third | 1 |
| Fourth | 0 |
| Fifth | 1 |
| Unassigned | 2 |
+------------+-------+
Note that the last entry is "unassigned", this is the number of records in the ticket table that DONT appear in the ticket_assigned table (thus being, unassigned). Also further note that user "Fourth" is zero, in that that user has no records in the ticket_assigned table.
Here is the current MySQL query I am using:
SELECT
CASE
WHEN users.FirstName IS NULL
THEN 'Unassigned'
ELSE users.FirstName
END as 'UserName',
COUNT(*) as 'TicketCount'
FROM tickets
LEFT OUTER JOIN ticket_assigned ON tickets.ticket_id = ticket_assigned.ticket_id
LEFT OUTER JOIN users ON ticket_assigned.user_id = users.user_id
GROUP BY ticket_assigned.user_id
ORDER BY UserName;
Problem with this is that it's not showing any of the users that don't feature in the ticket_assigned table, I'm essentially getting this:
+------------+-------+
| Name | Count |
+------------+-------+
| First | 2 |
| Second | 1 |
| Third | 1 |
| Fifth | 1 |
| Unassigned | 2 |
+------------+-------+
Is anyone able to assist and tell me how I can modify my query to include users that have no records in the ticket_assigned table? Thanks in advance!
Use a LEFT JOIN with a subquery to aggregate tickets:
SELECT t1.FirstName,
COALESCE(t2.ticket_count, 0) AS num_tickets
FROM users t1
LEFT JOIN
(
SELECT UserID, COUNT(*) AS ticket_count
FROM ticket_assigned
GROUP BY UserID
) t2
ON t1.ID = t2.UserID
UNION ALL
SELECT 'Unassigned', COUNT(*)
FROM tickets t
WHERE NOT EXISTS (SELECT 1 FROM tickets_assigned ta
WHERE ta.ticketId = t.id)
In MySQL, I think you need a left join and union all:
select u.id, u.firstname, count(ta.userId) as num_tickets
from users u left join
tickets_assigned ta
on ta.userId = u.id
group by u.id, u.firstname
union all
select NULL, 'Unassigned', count(*)
from tickets t
where not exists (select 1
from tickets_assigned
where ta.ticketId = t.id
);
I included the u.id in the aggregations. I'm uncomfortable just aggregating (and reporting) by first name, because different people frequently have the same first name, even in a relatively small group.
SELECT
u2.Firstname, IFNULL(tmp.count, 0) AS count
FROM users u2
LEFT JOIN (
SELECT u.id, u.Firstname, COUNT(1) as count
FROM ticket_assigned ta
LEFT JOIN ticket t ON t.id = ta.ticketID
LEFT JOIN users u ON u.id = ta.userID
GROUP BY u.id
) tmp ON tmp.id = u2.id
UNION
SELECT
'Unassigned', count(1) AS count
FROM ticket
WHERE id NOT IN (SELECT ticketid FROM ticket_assigned)
I have 2 tables, products and origins
Products:
p_id | name | origin_id
------------------------
1 | P1 | 1
2 | P2 | 2
3 | P3 | 1
Origins:
o_id | name
-------------
1 | O1
2 | O2
I am using the following query :
SELECT * FROM `products` LEFT OUTER JOIN `origins`
ON ( `products`.`origin_id` = `origins`.`o_id` ) LIMIT 2
I am getting the below results
p_id | name | origin_id | o_id | name
-----------------------------------------
1 | P1 | 1 | 1 | O1
3 | P3 | 1 | 1 | O1
I was wondering how the LEFT OUTER JOIN affects the result where I am getting the first and the third row rather than the first and the second row?
When you are not using ORDER BY Clause, there is no guarantee of a specific order for your SELECT query.
So we should use ORDER BY when we need any specific order.
See this: MySQL Ref: What is The Default Sort Order of SELECT with no ORDER BY Clause
You don't control the inherent ordering of rows in a table. It behaves like a set. If you want to order it, use order by clause.
SELECT * FROM `products` p LEFT OUTER JOIN `origins` o
ON ( p.`origin_id` = o.`o_id` ) ORDER BY p.`name` LIMIT 2
Output :
p_id | name | origin_id | o_id | name
-----------------------------------------
1 | P1 | 1 | 1 | O1
2 | P2 | 2 | 2 | O2