I have two tables Employee and Dept as below
EIN | ENAME | Salary | DeptID
1 | Ravi | 500 | 10
2 | Krishna | 1000 | 20
3 | Kiran | 1500 | 20
DeptID | DeptName
10 | IT
20 | Finance
I want the output as employees along with Deptname who is getting maximum salary group by dept
Here is an option which does not use analytic functions:
SELECT e.ENAME,
COALESCE(d.DeptName, 'NA') AS DeptName,
t.max_salary
FROM Employee e
LEFT JOIN Dept d
ON e.DeptID = d.DeptID
INNER JOIN
(
SELECT DeptID, MAX(SALARY) AS max_salary
FROM Employee
GROUP BY DeptId
) t
ON e.DeptID = t.DeptID AND
e.Salary = t.max_salary
Note that in the event that more than one employee should have the maximum salary in a given department, this query would return all ties. In the absence of further information, this seems reasonable without being able to distinguish one employee from another.
Update:
You could also use a WHERE clause containing a correlated subquery instead of joining to a (non-correlated) subquery as I gave above. Here is what that would look like:
SELECT e.ENAME,
COALESCE(d.DeptName, 'NA') AS DeptName,
e.Salary
FROM Employee e
LEFT JOIN Dept d
ON e.DeptID = d.DeptID
WHERE e.Salary = (SELECT MAX(t.Salary) FROM Employee t WHERE t.DeptID = e.DeptID)
However, I would recommend using the first option as it would probably perform better than the correlated subquery option.
Related
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;
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 two tables, one contains customers, the other one the bookings.
Now i want to see how many bookings come from one person but display it with their name instead of the id.
SELECT booking.id, COUNT(booking.id) AS idcount
FROM booking
GROUP BY booking.id ORDER BY idcount DESC;
The output is (correct count):
id | idcount
----------+--------
2 | 8
1 | 4
My attempt at getting the name displayed instead of the id was:
SELECT customer.lastn, customer.firstn, COUNT(booking.id) AS idcount
FROM booking, customer
GROUP BY customer.lastn, customer.firstn ORDER BY idcount DESC;
The output (wrong count):
lastn | firstn | idcount
----------+---------+--------
Adam | Michael | 13
Jackson | Leo | 13
13 is the total number of bookings (i just cut the output off) so there's that coming from, however i cant make the transition to get the right count with the name.
You need to use a JOIN in your FROM clause:
SELECT customer.lastn, customer.firstn, COUNT(booking.id) AS idcount
FROM booking
JOIN customer ON booking.id = customer.id
GROUP BY customer.lastn, customer.firstn
ORDER BY idcount DESC;
The JOIN here tells how the booking table relates to your customer table.
I have a single table laid out as such:
id | name | count
1 | John |
2 | Jim |
3 | John |
4 | Tim |
I need to fill out the count column such that the result is the number of times the specific name shows up in the column name.
The result should be:
id | name | count
1 | John | 2
2 | Jim | 1
3 | John | 2
4 | Tim | 1
I can get the count of occurrences of unique names easily using:
SELECT COUNT(name)
FROM table
GROUP BY name
But that doesn't fit into an UPDATE statement due to it returning multiple rows.
I can also get it narrowed down to a single row by doing this:
SELECT COUNT(name)
FROM table
WHERE name = 'John'
GROUP BY name
But that doesn't allow me to fill out the entire column, just the 'John' rows.
you can do that with a common table expression:
with counted as (
select name, count(*) as name_count
from the_table
group by name
)
update the_table
set "count" = c.name_count
from counted c
where c.name = the_table.name;
Another (slower) option would be to use a co-related sub-query:
update the_table
set "count" = (select count(*)
from the_table t2
where t2.name = the_table.name);
But in general it is a bad idea to store values that can easily be calculated on the fly:
select id,
name,
count(*) over (partition by name) as name_count
from the_table;
Another method : Using a derived table
UPDATE tb
SET count = t.count
FROM (
SELECT count(NAME)
,NAME
FROM tb
GROUP BY 2
) t
WHERE t.NAME = tb.NAME
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.