I am working at ROLAP on Oracle and i have this Fact Table :
Sales(market_id,item_id,sale), and i have this query :
SELECT market_id,item_id,SUM(sale) FROM Sales
GROUP BY CUBE(market_id,item_id);
Is there another way to get the same results but without using "CUBE" function ?
Te below query is an equivalent to a query with CUBE(market_id,item_id) clause (gives the same resultset).
But it will be slower, it will read the table 4 times - CUBE is optimized, it reads the table only once.
SELECT market_id,item_id,SUM(sale)
FROM Sales
GROUP BY market_id,item_id
UNION ALL
SELECT market_id,NULL,SUM(sale)
FROM Sales
GROUP BY market_id,NULL
UNION ALL
SELECT NULL,item_id,SUM(sale) FROM Sales
GROUP BY NULL,item_id
UNION ALL
SELECT NULL, NULL,SUM(sale)
FROM Sales
GROUP BY NULL, NULL
You can also solve it by using grouping_sets From Aggregation Function
and it will give you the same result
SELECT market_id,item_id,SUM(sale) FROM Sales
Group by GROUPING SETS ( (market_id,item_id) , (market_id)(item_id), () );
Related
Is it that pgadmin 4 does not support the execution of multiple select queries?
I tried executing this query
select cust, prod
from sales;
select *
from sales
it only showed me one table
You are missing semicolon after first query which is incorrect SQL syntax.
select cust, prod
from sales;
select *
from sales;
FYI, do not expect two separate results after executing it in query tool, you will only get result from last query only.
Updates for WITH clause question.
with Min_cust as (
select cust, max(quant),min(quant) from sales group by cust
),
FinalMin as (
select sales.cust,sales.prod,minium from sales
natural join Min_cust as A where sales.quant=A.min
)
select * from FinalMin;
In my table I have the columns id, userId and points. As a result of my query I would like to have the id of the record that contains the highest points, per user.
In my experience (more with MySQL than SQL Server) I would use the following query to get this result:
SELECT id, userId, max(points)
FROM table
GROUP BY userId
But SQL Server does not allow this, because all columns in the select should also be in the GROUP BY or be an aggregate function.
This is a hypothetical situation. My actual situation is a lot more complicated!
Use ROW_NUMBER window function in SQL Server
Select * from
(
select Row_Number() over(partition by userId Order by points desc) Rn,*
From yourtable
) A
Where Rn = 1
I have some sample data as follows
Name Value Timestamp
a 23 2016/12/23 11:23
a 43 2016/12/23 12:55
b 12 2016/12/23 12:55
I want to select the latest value for a and b. When I used Last_Value, I used the following query
Select Name, Last_Value(Value) over (partition by Name order by timestamp) from table
This returned 2 rows for a, but I wanted it grouped so that I get only the last entered value for each name. So I had to use sub queries.
select x.Name,x.Value from (Select Name, Last_Value(Value) over (partition by Name order by timestamp) ) as x group by x.Name,x.Value
This again returns 2 records for a...I just wanted to do a group by and orderby and instaed of selelcting the max() wanted to select the top record.
Can anybody tell me how to solve this problem?
One method doesn't use window functions:
select t.*
from table t
where t.timestamp = (select max(t2.timestamp) from table t2 where t2.name = t.name);
Otherwise, the subquery method is fine, although I would often use row_number() and conditional aggregation rather than last_value() (or first_value() with a descending order by).
Unfortunately, SQL Server does not support first_value() or last_value() as an aggregation function, only as a window function.
I need to retrieve all rows from a table where 2 columns combined are all different. So I want all the sales that do not have any other sales that happened on the same day for the same price. The sales that are unique based on day and price will get updated to an active status.
So I'm thinking:
UPDATE sales
SET status = 'ACTIVE'
WHERE id IN (SELECT DISTINCT (saleprice, saledate), id, count(id)
FROM sales
HAVING count = 1)
But my brain hurts going any farther than that.
SELECT DISTINCT a,b,c FROM t
is roughly equivalent to:
SELECT a,b,c FROM t GROUP BY a,b,c
It's a good idea to get used to the GROUP BY syntax, as it's more powerful.
For your query, I'd do it like this:
UPDATE sales
SET status='ACTIVE'
WHERE id IN
(
SELECT id
FROM sales S
INNER JOIN
(
SELECT saleprice, saledate
FROM sales
GROUP BY saleprice, saledate
HAVING COUNT(*) = 1
) T
ON S.saleprice=T.saleprice AND s.saledate=T.saledate
)
If you put together the answers so far, clean up and improve, you would arrive at this superior query:
UPDATE sales
SET status = 'ACTIVE'
WHERE (saleprice, saledate) IN (
SELECT saleprice, saledate
FROM sales
GROUP BY saleprice, saledate
HAVING count(*) = 1
);
Which is much faster than either of them. Nukes the performance of the currently accepted answer by factor 10 - 15 (in my tests on PostgreSQL 8.4 and 9.1).
But this is still far from optimal. Use a NOT EXISTS (anti-)semi-join for even better performance. EXISTS is standard SQL, has been around forever (at least since PostgreSQL 7.2, long before this question was asked) and fits the presented requirements perfectly:
UPDATE sales s
SET status = 'ACTIVE'
WHERE NOT EXISTS (
SELECT FROM sales s1 -- SELECT list can be empty for EXISTS
WHERE s.saleprice = s1.saleprice
AND s.saledate = s1.saledate
AND s.id <> s1.id -- except for row itself
)
AND s.status IS DISTINCT FROM 'ACTIVE'; -- avoid empty updates. see below
db<>fiddle here
Old sqlfiddle
Unique key to identify row
If you don't have a primary or unique key for the table (id in the example), you can substitute with the system column ctid for the purpose of this query (but not for some other purposes):
AND s1.ctid <> s.ctid
Every table should have a primary key. Add one if you didn't have one, yet. I suggest a serial or an IDENTITY column in Postgres 10+.
Related:
In-order sequence generation
Auto increment table column
How is this faster?
The subquery in the EXISTS anti-semi-join can stop evaluating as soon as the first dupe is found (no point in looking further). For a base table with few duplicates this is only mildly more efficient. With lots of duplicates this becomes way more efficient.
Exclude empty updates
For rows that already have status = 'ACTIVE' this update would not change anything, but still insert a new row version at full cost (minor exceptions apply). Normally, you do not want this. Add another WHERE condition like demonstrated above to avoid this and make it even faster:
If status is defined NOT NULL, you can simplify to:
AND status <> 'ACTIVE';
The data type of the column must support the <> operator. Some types like json don't. See:
How to query a json column for empty objects?
Subtle difference in NULL handling
This query (unlike the currently accepted answer by Joel) does not treat NULL values as equal. The following two rows for (saleprice, saledate) would qualify as "distinct" (though looking identical to the human eye):
(123, NULL)
(123, NULL)
Also passes in a unique index and almost anywhere else, since NULL values do not compare equal according to the SQL standard. See:
Create unique constraint with null columns
OTOH, GROUP BY, DISTINCT or DISTINCT ON () treat NULL values as equal. Use an appropriate query style depending on what you want to achieve. You can still use this faster query with IS NOT DISTINCT FROM instead of = for any or all comparisons to make NULL compare equal. More:
How to delete duplicate rows without unique identifier
If all columns being compared are defined NOT NULL, there is no room for disagreement.
The problem with your query is that when using a GROUP BY clause (which you essentially do by using distinct) you can only use columns that you group by or aggregate functions. You cannot use the column id because there are potentially different values. In your case there is always only one value because of the HAVING clause, but most RDBMS are not smart enough to recognize that.
This should work however (and doesn't need a join):
UPDATE sales
SET status='ACTIVE'
WHERE id IN (
SELECT MIN(id) FROM sales
GROUP BY saleprice, saledate
HAVING COUNT(id) = 1
)
You could also use MAX or AVG instead of MIN, it is only important to use a function that returns the value of the column if there is only one matching row.
If your DBMS doesn't support distinct with multiple columns like this:
select distinct(col1, col2) from table
Multi select in general can be executed safely as follows:
select distinct * from (select col1, col2 from table ) as x
As this can work on most of the DBMS and this is expected to be faster than group by solution as you are avoiding the grouping functionality.
I want to select the distinct values from one column 'GrondOfLucht' but they should be sorted in the order as given in the column 'sortering'. I cannot get the distinct values of just one column using
Select distinct GrondOfLucht,sortering
from CorWijzeVanAanleg
order by sortering
It will also give the column 'sortering' and because 'GrondOfLucht' AND 'sortering' is not unique, the result will be ALL rows.
use the GROUP to select the records of 'GrondOfLucht' in the order given by 'sortering
SELECT GrondOfLucht
FROM dbo.CorWijzeVanAanleg
GROUP BY GrondOfLucht, sortering
ORDER BY MIN(sortering)
I need to get some items from database with top three comments for each item.
Now I have two stored procedures GetAllItems and GetTopThreeeCommentsByItemId.
In application I get 100 items and then in foreach loop I call GetTopThreeeCommentsByItemId procedure to get top three comments.
I know that this is bad from performance standpoint.
Is there some technique that allows to get this with one query?
I can use OUTER APPLY to get one top comment (if any) but I don't know how to get three.
Items {ItemId, Title, Description, Price etc.}
Comments {CommentId, ItemId etc.}
Sample data that I want to get
Item_1
-- comment_1
-- comment_2
-- comment_3
Item_2
-- comment_4
-- comment_5
One approach would be to use a CTE (Common Table Expression) if you're on SQL Server 2005 and newer (you aren't specific enough in that regard).
With this CTE, you can partition your data by some criteria - i.e. your ItemId - and have SQL Server number all your rows starting at 1 for each of those "partitions", ordered by some criteria.
So try something like this:
;WITH ItemsAndComments AS
(
SELECT
i.ItemId, i.Title, i.Description, i.Price,
c.CommentId, c.CommentText,
ROW_NUMBER() OVER(PARTITION BY i.ItemId ORDER BY c.CommentId) AS 'RowNum'
FROM
dbo.Items i
LEFT OUTER JOIN
dbo.Comments c ON c.ItemId = i.ItemId
WHERE
......
)
SELECT
ItemId, Title, Description, Price,
CommentId, CommentText
FROM
ItemsAndComments
WHERE
RowNum <= 3
Here, I am selecting up to three entries (i.e. comments) for each "partition" (i.e. for each item) - ordered by the CommentId.
Does that approach what you're looking for??
You can write a single stored procedure which calls GetAllItems and GetTopThreeeCommentsByItemId, takes results in temp tables and join those tables to produce the single resultset you need.
If you do not have a chance to use a stored procedure, you can still do the same by running a single SQL script from data access tier, which calls GetAllItems and GetTopThreeeCommentsByItemId and takes results into temp tables and join them later to return a single resultset.
This gets two elder brother using OUTER APPLY:
select m.*, elder.*
from Member m
outer apply
(
select top 2 ElderBirthDate = x.BirthDate, ElderFirstname = x.Firstname
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc
) as elder
order by m.BirthDate, elder.ElderBirthDate desc
Source data:
create table Member
(
Firstname varchar(20) not null,
Lastname varchar(20) not null,
BirthDate date not null unique
);
insert into Member(Firstname,Lastname,Birthdate) values
('John','Lennon','Oct 9, 1940'),
('Paul','McCartney','June 8, 1942'),
('George','Harrison','February 25, 1943'),
('Ringo','Starr','July 7, 1940');
Output:
Firstname Lastname BirthDate ElderBirthDate ElderFirstname
-------------------- -------------------- ---------- -------------- --------------------
Ringo Starr 1940-07-07 NULL NULL
John Lennon 1940-10-09 1940-07-07 Ringo
Paul McCartney 1942-06-08 1940-10-09 John
Paul McCartney 1942-06-08 1940-07-07 Ringo
George Harrison 1943-02-25 1942-06-08 Paul
George Harrison 1943-02-25 1940-10-09 John
(6 row(s) affected)
Live test: http://www.sqlfiddle.com/#!3/19a63/2
marc's answer is better, just use OUTER APPLY if you need to query "near" entities (e.g. geospatial, elder brothers, nearest date to due date, etc) to the main entity.
Outer apply walkthrough: http://www.ienablemuch.com/2012/04/outer-apply-walkthrough.html
You might need DENSE_RANK instead of ROW_NUMBER/RANK though, as the criteria of a comment being a top could yield ties. TOP 1 could yield more than one, TOP 3 could yield more than three too. Example of that scenario(DENSE_RANK walkthrough): http://www.anicehumble.com/2012/03/postgresql-denserank.html
Its better that you select the statement by using the row_number statement and select the top 3 alone
select a.* from
(
Select *,row_number() over(partition by column)[dup]
) as a
where dup<=3