This question already has answers here:
Oracle SELECT TOP 10 records [duplicate]
(6 answers)
How do I do top 1 in Oracle? [duplicate]
(9 answers)
How do I limit the number of rows returned by an Oracle query after ordering?
(14 answers)
Fetch the rows which have the Max value for a column for each distinct value of another column
(35 answers)
Closed 5 years ago.
I need to select from two tables,
RATING_TABLE
RATING_TYPE RATING_PRIORITY
TITAN 1
PLATINUM(+) 1
PLATINUM 2
DIAMOND(+) 3
DIAMOND 3
GOLD 4
SILVER 4
RATING_STORAGE
RATING AMOUNT
SILVER 200
GOLD 510
DIAMOND 850
PLATINUM(+) 980
TITAN 5000
I want to select the rating from RATING_STORAGE table based on RATING_PRIORITY from RATING_TABLE.
I want to select one row with lowest rating priority. If two rating priority are eqaul I want to choose the one with the lowest amount.
So I used the query,
select s.rating,s.amount
from RATING_TABLE r, RATING_STORAGE s
where r.rating_type= s.rating_type
and rownum=1
order by r.rating_priority asc , s.amount asc ;
I am getting correct output when sorting the result but rownum=1 fails to give the topmost row.
Thanks in Advance.
You need to select after sorting is done, in your case:
select *
from (select s.rating
,s.amount
from rating_table r
,rating_storage s
where r.rating_type = s.rating_type
and rownum = 1
order by r.rating_priority asc
,s.amount asc)
where rownum = 1;
Related
This question already has answers here:
Fetch the rows which have the Max value for a column for each distinct value of another column
(35 answers)
Closed 5 months ago.
I am trying to get the newest order for each phone number so I used in oracle
select * from (select * from orders where phonenum ='914780' order by order_date)
where rownum<=1
it works for one number only if I used it of several number it give me wrong results
as each number has several orders
Use window function for ordering phone number wise orders and then pick each phone number latest record.
Select *
from (
Select o.*,
row_number() over (partition by phonenum order by order_id desc) AS rowno
from order o
Where phonenum = '1233'
) t
Where t.rowno = 1;
N.B.: use table name and columns according to your DB objects.
This question already has answers here:
How do I limit the number of rows returned by an Oracle query after ordering?
(14 answers)
Closed 4 years ago.
I have to limit to 2 rows.
But can't do it for a SQL-Fetch.
select *
from employee;
You can use something like this:
select *
from
( select *
from emp
order by data desc )
where ROWNUM <= 2;
You can change the query as:
select *
from
top_n_test
order by
num
fetch first 3 rows only;
The select first n rows only selects the first n rows.
Well, the simplest way is to
select *
from employee
where rownum <= 2;
but the question is what exactly do you want to do with that.
I have been working with an application that is integrated with spring and Hibernate 4.X.X and its transaction is managed by JTA in Weblogic application server. After 3 years, there are about 40 million records only into one table from 100 tables that exist in my DB. The DB is Oracle 11g. The response time of a query is about 5 minutes because of increasing the count of records of this tables.
I customized the query and put it into Sql Developer and run the query advisor plan for suggestion some Index. Totally after doing such this, its response time is reduced to 2 minute. But even so, this response time does not satisfy the Custumer. To further clarify I put the query, It is as following:
select *
from (select (count(storehouse0_.ID) over()) as col_0_0_,
storehouse3_.storeHouse_ID as col_1_0_,
(DBPK_PUB_STOREHOUSE.get_Storehouse_Title(storehouse5_.id, 1)) as col_2_0_,
storehouse5_.Organization_Code as col_3_0_,
publicgood1_.Goods_Item_Id as col_4_0_,
storehouse0_.storeHouse_Inventory_Id as col_5_0_,
storehouse0_.Id as col_6_0_,
storehouse3_.samapel_Item_Id as col_7_0_,
samapelite10_.MAINNAME as col_8_0_,
publicgood1_.serial_Number as col_9_0_,
publicgood1_1_.production_Year as col_10_0_,
samapelpar2_.ID_SourceInfo as col_11_0_,
samapelpar2_.Pn as col_12_0_,
storehouse3_.expire_Date as col_13_0_,
publicgood1_1_.Status_Id as col_14_0_,
baseinform12_.Topic as col_15_0_,
publicgood1_.public_Num as col_16_0_,
cast(publicgood1_1_.goods_Status as number(10, 0)) as col_17_0_,
publicgood1_1_.goods_Status as col_18_0_,
publicgood1_1_.deleted as col_19_0_
from amd.Core_StoreHouse_Inventory_Item storehouse0_,
amd.Core_STOREHOUSE_INVENTORY storehouse3_,
amd.Core_STOREHOUSE storehouse5_,
amd.SMP_SAMAPEL_CODE samapelite10_
cross join amd.Core_Goods_Item_Public publicgood1_
inner join amd.Core_Goods_Item publicgood1_1_
on publicgood1_.Goods_Item_Id = publicgood1_1_.Id
left outer join amd.SMP_SOURCEINFO samapelpar2_
on publicgood1_1_.Samapel_Part_Number_Id =
samapelpar2_.ID_SourceInfo, amd.App_BaseInformation
baseinform12_
where not exists
(select ssec.samapelITem_id
from core_security_samapelitem ssec
inner join core_goods_item g
on ssec.samapelitem_id = g.samapel_item_id
where not exists (SELECT aa.groupid
FROM app_actiongroup aa
where aa.groupid in
(select au.groupid
from app_usergroup au
where au.userid = 1)
and aa.actionid = 9054)
and ssec.isenable = 1
and storehouse0_.goods_Item_ID = g.id)
and not exists
(select *
from CORE_POWER_SECURITY cps
where not exists (SELECT aa.groupid
FROM app_actiongroup aa
where aa.groupid in
(select au.groupid
from app_usergroup au
where au.userid = 1)
and aa.actionid = 9055)
and cps.inventory_id =
storehouse0_.storeHouse_Inventory_Id
and cps.goodsitemtype = 6)
and storehouse0_.storeHouse_Inventory_Id = storehouse3_.Id
and storehouse3_.storeHouse_ID = storehouse5_.Id
and storehouse3_.samapel_Item_Id = samapelite10_.MAINCODE
and publicgood1_1_.Status_Id = baseinform12_.ID
and 1 <> 2
and storehouse0_.goods_Item_ID = publicgood1_.Goods_Item_Id
and publicgood1_1_.edited = 0
and publicgood1_1_.deleted = 0
and (exists (select storehouse13_.Id
from amd.Core_STOREHOUSE storehouse13_
cross join amd.core_power power16_
cross join amd.core_power power17_
where storehouse5_.powerID = power16_.Id
and storehouse13_.powerID = power17_.Id
and (storehouse13_.Id in (741684217))
and storehouse13_.storeHouseType = 2
and (power16_.hierarchiCode like
power17_.hierarchiCode || '%')) or
(storehouse3_.storeHouse_ID in (741684217)) and
storehouse5_.storeHouseType = 1)
and (storehouse5_.storeHouse_Status not in (2, 3))
order by storehouse3_.samapel_Item_Id)
where rownum <= 10
[Note: This query is generated by Hibernate].
It is clear that order by 40 million holds so much time.
I find the main issue of this query. I omitted the “order by” and run the query, its response time was reduced to about 5 second. I was wonderful why the “order by” affects so much the response time.
(Some body may think that if this table is partitioned or use another facility of oracle, it may get better response time. Ok it may be right but my emphasis is the “order by” performance. If there is a way that do the “order by” responsibility, why not to do it). Any way I am not able to omit the “order by” because the Customer needs to order and it is necessary for paging. I find a solution that is explained by an example. This solution I order only some records that is needed. How, I will explain later. It is clear when oracle wants to sort 40 million records, it naturally takes so much time. I replace “order by” with “where clause”. With doing this replacement the response time was reduces from 2 minute to about 5 second and this is very exciting for me.
I explain my solution via an example, anybody that read this Post tells me whether this solution is good or there are another solution that I do not know exists.
Another hand I have a solution that is explained later, if it is ok or not. Whether I use it or not.
I explain my solution:
Let’s assumed that there are two table as below:
Post table
Id Others fields
1
2
3
4
5
… …
Post_comment table
Id post_id
1 5
2 5
3 5
4 5
6 5
7 2
8 2
9 2
10 3
11 1
12 1
13 1
14 1
15 1
16 1
17 1
18 1
19 1
20 1
21 1
22 1
23 1
24 1
25 1
26 4
27 4
There is a form that shows the result of join between POST table and POST_COMMENT table.
I explain both query with “order by” all records of that table and “order by” only specific records that are needed. The result of two query are exactly the same but the response time of second approach is the better than that one.
You assume that the page size is 10 and you are in page 3.
The first query with the “order by” all records of that table:
select *
from (Select res.*, rownum as rownum_
from (Select * from POST_COMMENT Order by post_id asc) res
Where rownum <= 30)
where rownum_ > 20
The second solution:
Before execution the query, I query as below:
select *
from (select post_id, count(id) from POST_COMMENT group by post_id)
order by post_id asc
So the result of it is the below:
Post_id Count(id) Sum(count(id))
1 15 15
2 3 18
3 1 19
4 2 21
5 5 26
It needs to say that the third column that is "Sum(count(id))" is calculated after that query.Any entry of this column is sum all before records.
So there is a formula that specifics which post_id must be selected. The formula is the below:
pageSize = 10, pageNumber = 3
from : (pageNumber – 1) * pageCount 2 * 10 = 20
to : (pageNumber – 1) * pageCount + pageCount 20 + 10 = 30
So I need the posts that are between (20, 30] of Sum(count(id)). According to this, I need only two post_id that have value 4,5. According to this the main query of second approach is:
select *
from (select rownum as rownum_, res.*
from (select *
from (select * from POST_COMMENT where post_id in (4, 5))
order by post_id asc) res
where rownum <= 30)
where rownum_ > 20
If you look at both query, you will see the biggest difference. The second query only selects the records of POST_COMENT that have post_id that are 4 and 5. After that, orders this records not all records of that table.
After posting this post, I have searched. finally I am redirected to HERE . I can reach to the response time that is very excited for me. It is reduced from 3 minutes to less than 3 seconds. It is necessary to know, I only use one tip from all of the query optimization guidelines that are in that site that is Duplicate constant condition for different tables whenever possible.
Note: Before doing this tip, there are some indexs on fields that are in where-clause and order-by.
This question already has answers here:
Oracle select most recent date record
(4 answers)
Closed 5 years ago.
I want to select the latest record from a table as based on a date field (crtn_dt). The query below does not work. Does anyone have an idea how it should be fixed?
select * from parcels
order by crtn_dt desc
where rownum = 1
You'd need to order data in the subquery and filter them in an outer query.
select *
from (
select *
from parcels
order by crtn_dt desc
)
where rownum = 1
order by clause is among last operations to perform.
What your query does, apart from being semantically incorrect, it returns one (thanks to rownum = 1 predicate) arbitrary row, and then applies order by clause to that one row.
This question already has answers here:
Why does Oracle return specific sequence if 'orderby' values are identical?
(4 answers)
Closed 7 years ago.
All, Let's say the SQL looks like below.
Select a, b ,c from table1 order by c
If all the rows in table1 have the same field value in the field c. I want to know if the result has the same order for each time I executed the SQL.
Let's say data in the table1 looks like below.
a b c
-------------------------------------------
1 x1 2014-4-1
....
100 x100 2014-4-1
....
1000 x1000 2014-4-1
....
How Oracle determine the rows sequence for the same order by value?
Added
Will they be random sequence for each time?
One simple answer is NO. There is no guarantee that the ORDER BY on equal values will return the same sorted result every time. It might seem to you it is always stable, however, there are many reasons when it could change.
For example, the sorting on equal values might defer after:
Gathering statistics
Adding an index on the column
For example,
Let's say I have a table t:
SQL> SELECT * FROM t ORDER BY b;
A B
---------- ----------
1 1
2 1
3 2
4 2
5 3
6 3
6 rows selected.
The sorting on the column having similar values is just like:
SQL> CREATE TABLE t1 AS SELECT * FROM t ORDER BY b, DBMS_RANDOM.VALUE;
Table created.
SQL> SELECT * FROM t1 ORDER BY b;
A B
---------- ----------
1 1
2 1
4 2
3 2
5 3
6 3
6 rows selected.
So, similar data in bot the tables, however, ORDER BY on the column having equal values, dos not guarantee the same sorting.
They must not be random (change each time), but the order is not guaranteed (change sometimes).