This question already has answers here:
How ROWNUM works in pagination query?
(3 answers)
Closed 7 years ago.
I am new in PL/SQL and I am trying the ROWNUM keyword.
If I query this:
SELECT *
FROM my_table
WHERE ROWNUM <= 1
I am getting a result. Even in this case:
SELECT *
FROM my_table
WHERE ROWNUM = 1
But if I try
SELECT *
FROM my_table
WHERE ROWNUM = 2
I get an empty result..
But the table my_tablehas more than one tuple.
Can you help me?
Thank you!
ROWNUM is a psuedo column that has a value AFTER the result set is returned. Thus you can use where rownum < 2 but you can't select where ROWNUM equals a value because it does not have a value to compare to yet.
Related
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How ROWNUM works in pagination query?
(3 answers)
How do I limit the number of rows returned by an Oracle query after ordering?
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how to select even records from a table in oracle?
(12 answers)
Closed 2 years ago.
I'm attempting to access the 3rd row from the following query:
SELECT *
FROM (SELECT
OFFENSEDESC,
COUNT(*) AS num
FROM
CRIMEPROFILE
GROUP BY
OFFENSEDESC
ORDER BY num DESC) o
WHERE rownum = 3
However, it returns no rows, I am uncertain as to why that is, any help is appreciated. NOTE: ORACLE SQL
Try this
SELCT
OFFENSEDESC,
num
from
(
SELECT
OFFENSEDESC,
COUNT(*) AS num,
ROW_NUMBER() OVER (ORDER BY COUNT(*) DESC) as rnk
FROM
CRIMEPROFILE
GROUP BY
OFFENSEDESC
) val
WHERE rnk = 3
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 4 years ago.
I am trying to get the AMOUNT_APP WHERE DATE _APP is the greatest value.
I wrote this query, but I am having troubles
SELECT AMOUNT_APP
FROM Payments_App
WHERE DATE_APP = MAX(DATE_APP)
I expect to get 5234.34
My Table
Use order by and rownum:
select pa.amount_app
from (select pa.*
from payments_app
order by date_app desc
) pa
where rownum = 1;
Or keep can be quite efficient:
select max(pa.amount_app) keep (dense_rank first order by date_app desc)
from payments_app;
If we suppouse that DATE_APP is an attribute that you could find the most recently updated results.
select AMOUNT_APP FROM Payments_App WHERE DATE_APP = (Select
MAX(DATE_APP) FROM Payments_App) ;
This question already has answers here:
How ROWNUM works in pagination query?
(3 answers)
Closed 7 years ago.
I observed a strange behaviour with ROWNUM in Oracle with static tables. I am trying pagination with query like below
select * from (
select the_data,rownum as seqn from the_table
) where seqn <= somenumber and seqn >= othernumber
However when I execute query multiple times I observe that the rownum value returned is not unique for a row ie if a row appears at rownum 25 for the first time it appears at rownum 125 for second execution
This issue does not appear if I do a order by like,
select * from (
select the_data,rownum as seqn from the_table order by column3
) where seqn <= somenumber and seqn >= othernumber
However order by decreases performance. Is this normal or is there any other way to improve performance.
You should check oracle documents for this question. Followed links may be helpful for you http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions156.htm#SQLRF06100
One example:
SELECT * FROM ( SELECT ROW_NUMBER() OVER () AS R, T.* FROM T ) AS TR WHERE R <= 10;
T is a table name. R is a row
This question already has answers here:
How ROWNUM works in pagination query?
(3 answers)
Closed 3 years ago.
When I am using rownum and between keywords then the query doesn't return any rows. Can anyone explain the reason why query is not retrieving any rows?
select * from cus where rownum between 2 and 6;
I just want to check whether rownum will work when it is used with between keyword .So ,I just tried the above query to display the rows which are in between 2 and 6. But when I tried to execute the query, it doesn't retrieve any rows.
thanks in advance
Oracle rownum starts at 1, so you will never get the first rownum if you say between 2 and N.
It takes a row to "initiate" the rownum pseudocolumn sequence, so by eliminating rownum 1 in your criteria, you eliminate all rownums (or every row essentially has rownum 0).
Look at it like this. You don't get a ROWNUM until the database returns a row to you. The first row of any criteria will always be ROWNUM 1.
Now, the trick you can use is to use a subquery. Each subquery will have its own rownum, and if you alias it to another column name, you can preserve it into outer queries, and treat it however you like. So if you are looking to implement paging of a result set, you would normally alias rownum from inner results as rownum_ to an outer subquery to limit with BETWEEN.
select * from
(select t.*, rownum as rownum_ from t)
where rownum_ between 2 and 6
But note, that the outer result set will have its own rownum, so you could do:
select t2.*, rownum from
(select a, b, rownum as rownum_ from t) t2
where rownum_ between 2 and 6
You will see rownum on the final result still starts at 1, but your inner result will have rownum_ starting at 2.
select * from cus where rownum between 2 and 6;
That is completely wrong. Because, ROWNUM is a pseudo-column which increments to 2 only when it started at ROW one(random, of course). In your query, the predicate ROWNUM BETWEEN 2 AND 6 is meaningless, since ROWNUM has not yet been assigned.
Let's understand this step-by-step :
Understand how a SQL statement is interpreted. After the query is parsed, the filter is applied.
In your query, the filter ROWNUM BETWEEN 2 AND 6 is meaningless, since, Oracle has not yet assigned ROWNUM 1 as the first row is
not yet fetched.
When the first row is fetched, then ROWNUM is assigned as a pseudo-number. But the filter in your query directly points to rows
between 2 and 6, which is absurd. So, no rows are returned.
Mysql doesnt have rownum.
If you are looking for oracle maybe you can try something like this:
select * from (select cus.*, rownum as row_num from cus)
where row_num between 2 and 6;
or
select * from (select cus.*, rownum as row_num from cus)
where row_num >1 and row_num <=6;
This question already has answers here:
How to get records randomly from the oracle database?
(9 answers)
Closed 8 years ago.
I tried both these queries but none of them seem to work: I wish to fetch random rows from result set in oracle
select * from TABLE_NAME t where t.ent_application_id = 13101192 order
by Dbms_Random.Random
select * from TABLE_NAME t where t.ent_application_id = 13101192 order
by Dbms_Random.Value
Try
SELECT T.COLUMN1, T.COLUMN2, DBMS_RANDOM.VALUE
FROM TABLE_NAME T
WHERE T.ENT_APPLICATION_ID = 13101192
ORDER BY 3