Is there a way to make an Oracle query behave like it contains a MySQL limit clause?
In MySQL, I can do this:
select *
from sometable
order by name
limit 20,10
to get the 21st to the 30th rows (skip the first 20, give the next 10). The rows are selected after the order by, so it really starts on the 20th name alphabetically.
In Oracle, the only thing people mention is the rownum pseudo-column, but it is evaluated before order by, which means this:
select *
from sometable
where rownum <= 10
order by name
will return a random set of ten rows ordered by name, which is not usually what I want. It also doesn't allow for specifying an offset.
This question is related to
sql
oracle
pagination
sql-limit
An analytic solution with only one nested query:
SELECT * FROM
(
SELECT t.*, Row_Number() OVER (ORDER BY name) MyRow FROM sometable t
)
WHERE MyRow BETWEEN 10 AND 20;
Rank() could be substituted for Row_Number() but might return more records than you are expecting if there are duplicate values for name.
(untested) something like this may do the job
WITH
base AS
(
select * -- get the table
from sometable
order by name -- in the desired order
),
twenty AS
(
select * -- get the first 30 rows
from base
where rownum < 30
order by name -- in the desired order
)
select * -- then get rows 21 .. 30
from twenty
where rownum > 20
order by name -- in the desired order
There is also the analytic function rank, that you can use to order by.
Since version 12c Oracle supports the SQL:2008 Standard, which provides the following syntax to limit the SQL result set:
SELECT
title
FROM
post
ORDER BY
id DESC
FETCH FIRST 50 ROWS ONLY
Prior to version 12c, to fetch the Top-N records, you had to use a derived table and the ROWNUM pseudocolumn:
SELECT *
FROM (
SELECT
title
FROM
post
ORDER BY
id DESC
)
WHERE ROWNUM <= 50
An analytic solution with only one nested query:
SELECT * FROM
(
SELECT t.*, Row_Number() OVER (ORDER BY name) MyRow FROM sometable t
)
WHERE MyRow BETWEEN 10 AND 20;
Rank() could be substituted for Row_Number() but might return more records than you are expecting if there are duplicate values for name.
(untested) something like this may do the job
WITH
base AS
(
select * -- get the table
from sometable
order by name -- in the desired order
),
twenty AS
(
select * -- get the first 30 rows
from base
where rownum < 30
order by name -- in the desired order
)
select * -- then get rows 21 .. 30
from twenty
where rownum > 20
order by name -- in the desired order
There is also the analytic function rank, that you can use to order by.
Less SELECT statements. Also, less performance consuming. Credits to: [email protected]
SELECT *
FROM (SELECT t.*,
rownum AS rn
FROM shhospede t) a
WHERE a.rn >= in_first
AND a.rn <= in_first;
You can use a subquery for this like
select *
from
( select *
from emp
order by sal desc )
where ROWNUM <= 5;
Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.
Update: To limit the result with both lower and upper bounds things get a bit more bloated with
select * from
( select a.*, ROWNUM rnum from
( <your_query_goes_here, with order by> ) a
where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum >= :MIN_ROW_TO_FETCH;
(Copied from specified AskTom-article)
Update 2: Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
See this answer for more examples. Thanks to Krumia for the hint.
I'v started preparing for Oracle 1z0-047 exam, validated against 12c While prepping for it i came across a 12c enhancement known as 'FETCH FIRST' It enables you to fetch rows /limit rows as per your convenience. Several options are available with it
- FETCH FIRST n ROWS ONLY
- OFFSET n ROWS FETCH NEXT N1 ROWS ONLY // leave the n rows and display next N1 rows
- n % rows via FETCH FIRST N PERCENT ROWS ONLY
Example:
Select * from XYZ a
order by a.pqr
FETCH FIRST 10 ROWS ONLY
Less SELECT statements. Also, less performance consuming. Credits to: [email protected]
SELECT *
FROM (SELECT t.*,
rownum AS rn
FROM shhospede t) a
WHERE a.rn >= in_first
AND a.rn <= in_first;
You can use a subquery for this like
select *
from
( select *
from emp
order by sal desc )
where ROWNUM <= 5;
Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.
Update: To limit the result with both lower and upper bounds things get a bit more bloated with
select * from
( select a.*, ROWNUM rnum from
( <your_query_goes_here, with order by> ) a
where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum >= :MIN_ROW_TO_FETCH;
(Copied from specified AskTom-article)
Update 2: Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
See this answer for more examples. Thanks to Krumia for the hint.
Since version 12c Oracle supports the SQL:2008 Standard, which provides the following syntax to limit the SQL result set:
SELECT
title
FROM
post
ORDER BY
id DESC
FETCH FIRST 50 ROWS ONLY
Prior to version 12c, to fetch the Top-N records, you had to use a derived table and the ROWNUM pseudocolumn:
SELECT *
FROM (
SELECT
title
FROM
post
ORDER BY
id DESC
)
WHERE ROWNUM <= 50
I'v started preparing for Oracle 1z0-047 exam, validated against 12c While prepping for it i came across a 12c enhancement known as 'FETCH FIRST' It enables you to fetch rows /limit rows as per your convenience. Several options are available with it
- FETCH FIRST n ROWS ONLY
- OFFSET n ROWS FETCH NEXT N1 ROWS ONLY // leave the n rows and display next N1 rows
- n % rows via FETCH FIRST N PERCENT ROWS ONLY
Example:
Select * from XYZ a
order by a.pqr
FETCH FIRST 10 ROWS ONLY
If you are not on Oracle 12C, you can use TOP N query like below.
SELECT *
FROM
( SELECT rownum rnum
, a.*
FROM sometable a
ORDER BY name
)
WHERE rnum BETWEEN 10 AND 20;
You can even move this from clause in with clause as follows
WITH b AS
( SELECT rownum rnum
, a.*
FROM sometable a ORDER BY name
)
SELECT * FROM b
WHERE rnum BETWEEN 10 AND 20;
Here actually we are creating a inline view and renaming rownum as rnum. You can use rnum in main query as filter criteria.
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID=5
greater then values find out
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID>5
less then values find out
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID=5
For each row returned by a query, the ROWNUM pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a ROWNUM of 1, the second has 2, and so on.
SELECT * FROM sometable1 so
WHERE so.id IN (
SELECT so2.id from sometable2 so2
WHERE ROWNUM <=5
)
AND ORDER BY so.somefield AND ROWNUM <= 100
I have implemented this in oracle server 11.2.0.1.0
You can use a subquery for this like
select *
from
( select *
from emp
order by sal desc )
where ROWNUM <= 5;
Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.
Update: To limit the result with both lower and upper bounds things get a bit more bloated with
select * from
( select a.*, ROWNUM rnum from
( <your_query_goes_here, with order by> ) a
where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum >= :MIN_ROW_TO_FETCH;
(Copied from specified AskTom-article)
Update 2: Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
See this answer for more examples. Thanks to Krumia for the hint.
If you are not on Oracle 12C, you can use TOP N query like below.
SELECT *
FROM
( SELECT rownum rnum
, a.*
FROM sometable a
ORDER BY name
)
WHERE rnum BETWEEN 10 AND 20;
You can even move this from clause in with clause as follows
WITH b AS
( SELECT rownum rnum
, a.*
FROM sometable a ORDER BY name
)
SELECT * FROM b
WHERE rnum BETWEEN 10 AND 20;
Here actually we are creating a inline view and renaming rownum as rnum. You can use rnum in main query as filter criteria.
(untested) something like this may do the job
WITH
base AS
(
select * -- get the table
from sometable
order by name -- in the desired order
),
twenty AS
(
select * -- get the first 30 rows
from base
where rownum < 30
order by name -- in the desired order
)
select * -- then get rows 21 .. 30
from twenty
where rownum > 20
order by name -- in the desired order
There is also the analytic function rank, that you can use to order by.
You can use a subquery for this like
select *
from
( select *
from emp
order by sal desc )
where ROWNUM <= 5;
Have also a look at the topic On ROWNUM and limiting results at Oracle/AskTom for more information.
Update: To limit the result with both lower and upper bounds things get a bit more bloated with
select * from
( select a.*, ROWNUM rnum from
( <your_query_goes_here, with order by> ) a
where ROWNUM <= :MAX_ROW_TO_FETCH )
where rnum >= :MIN_ROW_TO_FETCH;
(Copied from specified AskTom-article)
Update 2: Starting with Oracle 12c (12.1) there is a syntax available to limit rows or start at offsets.
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
See this answer for more examples. Thanks to Krumia for the hint.
Pagination queries with ordering are really tricky in Oracle.
Oracle provides a ROWNUM pseudocolumn that returns a number indicating the order in which the database selects the row from a table or set of joined views.
ROWNUM is a pseudocolumn that gets many people into trouble. A ROWNUM value is not permanently assigned to a row (this is a common misunderstanding). It may be confusing when a ROWNUM value is actually assigned. A ROWNUM value is assigned to a row after it passes filter predicates of the query but before query aggregation or sorting.
What is more, a ROWNUM value is incremented only after it is assigned.
This is why the followin query returns no rows:
select *
from (select *
from some_table
order by some_column)
where ROWNUM <= 4 and ROWNUM > 1;
The first row of the query result does not pass ROWNUM > 1 predicate, so ROWNUM does not increment to 2. For this reason, no ROWNUM value gets greater than 1, consequently, the query returns no rows.
Correctly defined query should look like this:
select *
from (select *, ROWNUM rnum
from (select *
from skijump_results
order by points)
where ROWNUM <= 4)
where rnum > 1;
Find out more about pagination queries in my articles on Vertabelo blog:
In case of SQL-Developer, it automatically fetches only first 50 rows. And if we scroll down, it fetches another 50 rows and so on !
Hence we dont need to define, in case of sql-developer tool !
I did some performance testing for the following approaches:
select * from (
select a.*, ROWNUM rnum from (
<select statement with order by clause>
) a where rownum <= MAX_ROW
) where rnum >= MIN_ROW
select * from (
<select statement with order by clause>
) where myrow between MIN_ROW and MAX_ROW
select * from (
select statement, rownum as RN with order by clause
) where a.rn >= MIN_ROW and a.rn <= MAX_ROW
Table had 10 million records, sort was on an unindexed datetime row:
Selecting first 10 rows took:
Selecting rows between 100,000 and 100,010:
Selecting rows between 9,000,000 and 9,000,010:
For each row returned by a query, the ROWNUM pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a ROWNUM of 1, the second has 2, and so on.
SELECT * FROM sometable1 so
WHERE so.id IN (
SELECT so2.id from sometable2 so2
WHERE ROWNUM <=5
)
AND ORDER BY so.somefield AND ROWNUM <= 100
I have implemented this in oracle server 11.2.0.1.0
An analytic solution with only one nested query:
SELECT * FROM
(
SELECT t.*, Row_Number() OVER (ORDER BY name) MyRow FROM sometable t
)
WHERE MyRow BETWEEN 10 AND 20;
Rank() could be substituted for Row_Number() but might return more records than you are expecting if there are duplicate values for name.
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID=5
greater then values find out
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID>5
less then values find out
select * FROM (SELECT
ROW_NUMBER() OVER (ORDER BY sal desc),* AS ROWID,
FROM EMP ) EMP where ROWID=5
(untested) something like this may do the job
WITH
base AS
(
select * -- get the table
from sometable
order by name -- in the desired order
),
twenty AS
(
select * -- get the first 30 rows
from base
where rownum < 30
order by name -- in the desired order
)
select * -- then get rows 21 .. 30
from twenty
where rownum > 20
order by name -- in the desired order
There is also the analytic function rank, that you can use to order by.
On Oracle 12c (see row limiting clause in SQL reference):
SELECT *
FROM sometable
ORDER BY name
OFFSET 20 ROWS FETCH NEXT 10 ROWS ONLY;
I did some performance testing for the following approaches:
select * from (
select a.*, ROWNUM rnum from (
<select statement with order by clause>
) a where rownum <= MAX_ROW
) where rnum >= MIN_ROW
select * from (
<select statement with order by clause>
) where myrow between MIN_ROW and MAX_ROW
select * from (
select statement, rownum as RN with order by clause
) where a.rn >= MIN_ROW and a.rn <= MAX_ROW
Table had 10 million records, sort was on an unindexed datetime row:
Selecting first 10 rows took:
Selecting rows between 100,000 and 100,010:
Selecting rows between 9,000,000 and 9,000,010:
Pagination queries with ordering are really tricky in Oracle.
Oracle provides a ROWNUM pseudocolumn that returns a number indicating the order in which the database selects the row from a table or set of joined views.
ROWNUM is a pseudocolumn that gets many people into trouble. A ROWNUM value is not permanently assigned to a row (this is a common misunderstanding). It may be confusing when a ROWNUM value is actually assigned. A ROWNUM value is assigned to a row after it passes filter predicates of the query but before query aggregation or sorting.
What is more, a ROWNUM value is incremented only after it is assigned.
This is why the followin query returns no rows:
select *
from (select *
from some_table
order by some_column)
where ROWNUM <= 4 and ROWNUM > 1;
The first row of the query result does not pass ROWNUM > 1 predicate, so ROWNUM does not increment to 2. For this reason, no ROWNUM value gets greater than 1, consequently, the query returns no rows.
Correctly defined query should look like this:
select *
from (select *, ROWNUM rnum
from (select *
from skijump_results
order by points)
where ROWNUM <= 4)
where rnum > 1;
Find out more about pagination queries in my articles on Vertabelo blog:
An analytic solution with only one nested query:
SELECT * FROM
(
SELECT t.*, Row_Number() OVER (ORDER BY name) MyRow FROM sometable t
)
WHERE MyRow BETWEEN 10 AND 20;
Rank() could be substituted for Row_Number() but might return more records than you are expecting if there are duplicate values for name.
As an extension of accepted answer Oracle internally uses ROW_NUMBER/RANK functions. OFFSET FETCH syntax is a syntax sugar.
It could be observed by using DBMS_UTILITY.EXPAND_SQL_TEXT procedure:
Preparing sample:
CREATE TABLE rownum_order_test (
val NUMBER
);
INSERT ALL
INTO rownum_order_test
SELECT level
FROM dual
CONNECT BY level <= 10;
COMMIT;
Query:
SELECT val
FROM rownum_order_test
ORDER BY val DESC
FETCH FIRST 5 ROWS ONLY;
is regular:
SELECT "A1"."VAL" "VAL"
FROM (SELECT "A2"."VAL" "VAL","A2"."VAL" "rowlimit_$_0",
ROW_NUMBER() OVER ( ORDER BY "A2"."VAL" DESC ) "rowlimit_$$_rownumber"
FROM "ROWNUM_ORDER_TEST" "A2") "A1"
WHERE "A1"."rowlimit_$$_rownumber"<=5 ORDER BY "A1"."rowlimit_$_0" DESC;
Fetching expanded SQL text:
declare
x VARCHAR2(1000);
begin
dbms_utility.expand_sql_text(
input_sql_text => '
SELECT val
FROM rownum_order_test
ORDER BY val DESC
FETCH FIRST 5 ROWS ONLY',
output_sql_text => x);
dbms_output.put_line(x);
end;
/
WITH TIES is expanded as RANK:
declare
x VARCHAR2(1000);
begin
dbms_utility.expand_sql_text(
input_sql_text => '
SELECT val
FROM rownum_order_test
ORDER BY val DESC
FETCH FIRST 5 ROWS WITH TIES',
output_sql_text => x);
dbms_output.put_line(x);
end;
/
SELECT "A1"."VAL" "VAL"
FROM (SELECT "A2"."VAL" "VAL","A2"."VAL" "rowlimit_$_0",
RANK() OVER ( ORDER BY "A2"."VAL" DESC ) "rowlimit_$$_rank"
FROM "ROWNUM_ORDER_TEST" "A2") "A1"
WHERE "A1"."rowlimit_$$_rank"<=5 ORDER BY "A1"."rowlimit_$_0" DESC
and offset:
declare
x VARCHAR2(1000);
begin
dbms_utility.expand_sql_text(
input_sql_text => '
SELECT val
FROM rownum_order_test
ORDER BY val
OFFSET 4 ROWS FETCH NEXT 4 ROWS ONLY',
output_sql_text => x);
dbms_output.put_line(x);
end;
/
SELECT "A1"."VAL" "VAL"
FROM (SELECT "A2"."VAL" "VAL","A2"."VAL" "rowlimit_$_0",
ROW_NUMBER() OVER ( ORDER BY "A2"."VAL") "rowlimit_$$_rownumber"
FROM "ROWNUM_ORDER_TEST" "A2") "A1"
WHERE "A1"."rowlimit_$$_rownumber"<=CASE WHEN (4>=0) THEN FLOOR(TO_NUMBER(4))
ELSE 0 END +4 AND "A1"."rowlimit_$$_rownumber">4
ORDER BY "A1"."rowlimit_$_0"
In case of SQL-Developer, it automatically fetches only first 50 rows. And if we scroll down, it fetches another 50 rows and so on !
Hence we dont need to define, in case of sql-developer tool !
Source: Stackoverflow.com