This is db query .
select users.Id,jsonb_object_keys(orders.metadata::jsonb) from users left join orders on users.userId=orders.userId where users.userId=2;
users table orders table
------------------- -----------------------------------------------------
|userId| name | | userId|orderId|metadata |
| 1 | john | | 1 | 1 | {"orderName":"chess","quantity":1}|
| 2 | doe | | 1 | 2 | {"orderName":"cube" ,"quantity":1}|
------------------- -----------------------------------------------------
Why there are no rows returned by the query ?
Very Nice and tricky question. to achieve what you want you should try below query:
select
t1.userid,
t2.keys
from
users t1
left join (select userid, orderid, jsonb_object_keys(metadata) as keys from orders) t2
on t1.userid=t2.userid
Your Query seems correct but there is catch. When you are left joining both tables without jsonb_object_keys(metadata), it will work as you are expecting. But when you use with this function then this function will return a set of records for each rows of select statement and perform simple join with rest of the columns internally. That's why it will remove the rows having NULL value in second column.
You should left join to the result of the jsonb_each() call:
select users.userid, meta.*
from users
left join orders on users.userid = orders.userid
left join jsonb_object_keys(orders.metadata::jsonb) as meta on true
where users.userid = 2;
Related
I have two tables
The first table contains three text fields(username, email, num) the second have only one column with random birth_date DATE.
I need to merge tables without condition
For example
first table:
+----------+--------------+-----------+
| username | email | num |
+----------+--------------+-----------+
| 'user1' | 'user1#mail' | '+794949' |
| 'user2' | 'user2#mail' | '+799999' |
+----------+--------------+-----------+
second table:
+--------------+
| birth_date |
+--------------+
| '2001-01-01' |
| '2002-02-02' |
+--------------+
And I need result like
+----------+------------+-------------+--------------+
| username | email | num | birth_date |
+----------+------------+-------------+--------------+
| 'user1' | 'us1#mail' | '+7979797' | '2001-01-01' |
| 'user2' | 'us2#mail' | '+79898998' | '2002-02-02' |
+----------+------------+-------------+--------------+
I need to get in result table with 100 rows too
Tried different JOIN but there is no condition here
Sure there is a join condition, about the simplest there is: Join on true or cross join. Either is the basic merge tables without condition. However this does not result in what you want as it generates a result set of 10k rows. But you an then use limit:
select *
from table1
join table2 on true
order by random()
limit 100;
select *
from table1
cross join table2
order by random()
limit 100;
There is other option, witch I think may be closer to what you want. Assign a value to each row of each table. Then join on this assigned value:
select <column list>
from (select *, row_number() over() rn from table1) t1
join (select *, row_number() over() rn from table2) t2
on (t1.rn = t2.rn);
To eliminate the assigned value you must specifically list each column desired in the result. But that is the way it should be done anyway.
See demo here. (demo user just 3 rows instead of 100)
So, I have 2 tables,
In the 1st table, there is an Information of users
user_id | name
1 | Albert
2 | Anthony
and in the other table, I have information
where some users have address information where it can either be home, office or both home and office
user_id| address_type | address
1 | home | a
1 | office | b
2 | home | c
and the final result I want is this
user_id | name | home_address | office_address
1 | Albert | a | b
2 | Anthony | c | null
I have tried using left join and json_agg but the information that way is not readable,
any suggestions on how I can do this?
You can use two outer joins, one for the office address and one for the home address.
select t1.user_id, t1.name,
ha.address as home_address,
oa.address as office_address
from table1 t1
left join table2 ha on ha.user_id = t1.user_id and ha.address_type = 'home'
left join table2 oa on oa.user_id = t1.user_id and ha.address_type = 'office';
A solution using JSON could look like this
select t1.user_id, t1.name,
a.addresses ->> 'home' as home_address,
a.addresses ->> 'office' as office_address
from table1 t1
left join (
select user_id, jsonb_object_agg(address_type, address) as addresses
from table2
group by user_id
) a on a.user_id = t1.user_id;
Which might be a bit more flexible, because you don't need to add a new join for each address type. The first query is likely to be faster if you need to retrieve a large number of rows.
I'm new to SQL but I'm trying to join two tables. However, it's not working as I expected. This is in Postgresql.
Here are the tables I'm trying to join.
My Tables
SELECT * FROM houses;
id | name | address | picture
----+----------------+-------------+------------
1 | House 1 | 440 S 3rd W | long-link2.jpg
2 | House 2 | 538 S 5th E | long-link.jpg
SELECT house_id, trunc(avg(score), 1) FROM house_reviews GROUP BY house_id;
house_id | trunc
----------+-------
1 | 3.0
2 | 3.0
My JOIN statements
Attempt 1 (works)
SELECT * FROM houses
LEFT JOIN (SELECT house_id, trunc(avg(score), 1) FROM house_reviews GROUP BY house_id) AS r
ON houses.id = r.house_id;
Attempt 2 (does not work)
SELECT id, name, address FROM houses
LEFT JOIN (SELECT house_id, trunc(avg(score), 1) FROM house_reviews GROUP BY house_id) AS r
ON houses.id = r.house_id;
The only difference between the two is that I don't select the picture in the attempt 2. But attempt 2 doesn't seem to join at all. Instead it displays
id | name | address
----+----------------+-------------
1 | Tuscany | 440 S 2nd W
2 | Mountain Lofts | 538 S 2nd W
meaning that it failed to join and is instead just displaying the houses table.
My Question
I'm confused why the join failed in the second table because I removed only one arbitrary column (pictures).
Is there a way that I can join the two tables together but also exclude the pictures column from the "houses" table?
Thank you!
You're only seeing data from houses because that's all you've selected. Try this:
SELECT
h.id, h.name, h.address,
r.avg_score
FROM houses h
LEFT JOIN (
SELECT house_id, trunc(avg(score), 1) avg_score
FROM house_reviews
GROUP BY house_id
) AS r
ON houses.id = r.house_id;
Let's say I have this 3 tables
Countries ProvOrStates MajorCities
-----+------------- -----+----------- -----+-------------
Id | CountryName Id | CId | Name Id | POSId | Name
-----+------------- -----+----------- -----+-------------
1 | USA 1 | 1 | NY 1 | 1 | NYC
How do you get something like
---------------------------------------------
CountryName | ProvinceOrState | MajorCities
| (Count) | (Count)
---------------------------------------------
USA | 50 | 200
---------------------------------------------
Canada | 10 | 57
So far, the way I see it:
Run the first SELECT COUNT (GROUP BY Countries.Id) on Countries JOIN ProvOrStates,
store the result in a table variable,
Run the second SELECT COUNT (GROUP BY Countries.Id) on ProvOrStates JOIN MajorCities,
Update the table variable based on the Countries.Id
Join the table variable with Countries table ON Countries.Id = Id of the table variable.
Is there a possibility to run just one query instead of multiple intermediary queries? I don't know if it's even feasible as I've tried with no luck.
Thanks for helping
Use sub query or derived tables and views
Basically If You You Have 3 Tables
select * from [TableOne] as T1
join
(
select T2.Column, T3.Column
from [TableTwo] as T2
join [TableThree] as T3
on T2.CondtionColumn = T3.CondtionColumn
) AS DerivedTable
on T1.DepName = DerivedTable.DepName
And when you are 100% percent sure it's working you can create a view that contains your three tables join and call it when ever you want
PS: in case of any identical column names or when you get this message
"The column 'ColumnName' was specified multiple times for 'Table'. "
You can use alias to solve this problem
This answer comes from #lotzInSpace.
SELECT ct.[CountryName], COUNT(DISTINCT p.[Id]), COUNT(DISTINCT c.[Id])
FROM dbo.[Countries] ct
LEFT JOIN dbo.[Provinces] p
ON ct.[Id] = p.[CountryId]
LEFT JOIN dbo.[Cities] c
ON p.[Id] = c.[ProvinceId]
GROUP BY ct.[CountryName]
It's working. I'm using LEFT JOIN instead of INNER JOIN because, if a country doesn't have provinces, or a province doesn't have cities, then that country or province doesn't display.
Thanks again #lotzInSpace.
I have a group by query which fetches me some records. What if I wish to find other column details representing those records.
Suppose I have a query as follows .Select id,max(date) from records group by id;
to fetch the most recent entry in the table.
I wish to fetch another column representing those records .
I want to do something like this (This incorrect query is just for example) :
Select type from (Select id,max(date) from records group by id) but here type doesnt exist in the inner query.
I am not able to define the question in a simpler manner.I Apologise for that.
Any help is appreciated.
EDIT :
Column | Type | Modifiers
--------+-----------------------+-----------
id | integer |
rdate | date |
type | character varying(20) |
Sample Data :
id | rdate | type
----+------------+------
1 | 2013-11-03 | E1
1 | 2013-12-12 | E1
2 | 2013-12-12 | A3
3 | 2014-01-11 | B2
1 | 2014-01-15 | A1
4 | 2013-12-23 | C1
5 | 2014-01-05 | C
7 | 2013-12-20 | D
8 | 2013-12-20 | D
9 | 2013-12-23 | A1
While I was trying something like this (I'm no good at sql) : select type from records as r1 inner join (Select id,max(rdate) from records group by id) r2 on r1.rdate = r2.rdate ;
or
select type from records as r1 ,(Select id,max(rdate) from records group by id) r2 inner join r1 on r1.rdate = r2.rdate ;
You can easily do this with a window function:
SELECT id, rdate, type
FROM (
SELECT id, rdate, type, rank() OVER (PARTITION BY id ORDER BY rdate DESC) rnk
FROM records
WHERE rnk = 1
) foo
ORDER BY id;
The window definition OVER (PARTITION BY id ORDER BY rdate DESC) takes all records with the same id value, then sorts then from most recent to least recent rdate and assigns a rank to each row. The rank of 1 is the most recent, so equivalent to max(rdate).
If I've understood the question right, then this should work (or at least get you something you can work with):
SELECT
b.id, b.maxdate, a.type
FROM
records a -- this is the records table, where you'll get the type
INNER JOIN -- now join it to the group by query
(select id, max(rdate) as maxdate FROM records GROUP BY id) b
ON -- join on both rdate and id, otherwise you'll get lots of duplicates
b.id = a.id
AND b.maxdate = a.rdate
Note that if you have records with different types for the same id and rdate combination you'll get duplicates.