I'm interested in learning some (ideally) database agnostic ways of selecting the nth row from a database table. It would also be interesting to see how this can be achieved using the native functionality of the following databases:
SQL Server
MySQL
PostgreSQL
SQLite
Oracle
I am currently doing something like the following in SQL Server 2005, but I'd be interested in seeing other's more agnostic approaches:
WITH Ordered AS (
SELECT ROW_NUMBER() OVER (ORDER BY OrderID) AS RowNumber, OrderID, OrderDate
FROM Orders)
SELECT *
FROM Ordered
WHERE RowNumber = 1000000
Credit for the above SQL: Firoz Ansari's Weblog
Update: See Troels Arvin's answer regarding the SQL standard. Troels, have you got any links we can cite?
There are ways of doing this in optional parts of the standard, but a lot of databases support their own way of doing it.
A really good site that talks about this and other things is http://troels.arvin.dk/db/rdbms/#select-limit.
Basically, PostgreSQL and MySQL supports the non-standard:
SELECT...
LIMIT y OFFSET x
Oracle, DB2 and MSSQL supports the standard windowing functions:
SELECT * FROM (
SELECT
ROW_NUMBER() OVER (ORDER BY key ASC) AS rownumber,
columns
FROM tablename
) AS foo
WHERE rownumber <= n
(which I just copied from the site linked above since I never use those DBs)
Update: As of PostgreSQL 8.4 the standard windowing functions are supported, so expect the second example to work for PostgreSQL as well.
Update: SQLite added window functions support in version 3.25.0 on 2018-09-15 so both forms also work in SQLite.
PostgreSQL supports windowing functions as defined by the SQL standard, but they're awkward, so most people use (the non-standard) LIMIT / OFFSET:
SELECT
*
FROM
mytable
ORDER BY
somefield
LIMIT 1 OFFSET 20;
This example selects the 21st row. OFFSET 20 is telling Postgres to skip the first 20 records. If you don't specify an ORDER BY clause, there's no guarantee which record you will get back, which is rarely useful.
I'm not sure about any of the rest, but I know SQLite and MySQL don't have any "default" row ordering. In those two dialects, at least, the following snippet grabs the 15th entry from the_table, sorting by the date/time it was added:
SELECT *
FROM the_table
ORDER BY added DESC
LIMIT 1,15
(of course, you'd need to have an added DATETIME field, and set it to the date/time that entry was added...)
SQL 2005 and above has this feature built-in. Use the ROW_NUMBER() function. It is excellent for web-pages with a << Prev and Next >> style browsing:
Syntax:
SELECT
*
FROM
(
SELECT
ROW_NUMBER () OVER (ORDER BY MyColumnToOrderBy) AS RowNum,
*
FROM
Table_1
) sub
WHERE
RowNum = 23
I suspect this is wildly inefficient but is quite a simple approach, which worked on a small dataset that I tried it on.
select top 1 field
from table
where field in (select top 5 field from table order by field asc)
order by field desc
This would get the 5th item, change the second top number to get a different nth item
SQL server only (I think) but should work on older versions that do not support ROW_NUMBER().
Verify it on SQL Server:
Select top 10 * From emp
EXCEPT
Select top 9 * From emp
This will give you 10th ROW of emp table!
Contrary to what some of the answers claim, the SQL standard is not silent regarding this subject.
Since SQL:2003, you have been able to use "window functions" to skip rows and limit result sets.
And in SQL:2008, a slightly simpler approach had been added, using
OFFSET skip ROWS
FETCH FIRST n ROWS ONLY
Personally, I don't think that SQL:2008's addition was really needed, so if I were ISO, I would have kept it out of an already rather large standard.
1 small change: n-1 instead of n.
select *
from thetable
limit n-1, 1
SQL SERVER
Select n' th record from top
SELECT * FROM (
SELECT
ID, NAME, ROW_NUMBER() OVER(ORDER BY ID) AS ROW
FROM TABLE
) AS TMP
WHERE ROW = n
select n' th record from bottom
SELECT * FROM (
SELECT
ID, NAME, ROW_NUMBER() OVER(ORDER BY ID DESC) AS ROW
FROM TABLE
) AS TMP
WHERE ROW = n
When we used to work in MSSQL 2000, we did what we called the "triple-flip":
EDITED
DECLARE #InnerPageSize int
DECLARE #OuterPageSize int
DECLARE #Count int
SELECT #Count = COUNT(<column>) FROM <TABLE>
SET #InnerPageSize = #PageNum * #PageSize
SET #OuterPageSize = #Count - ((#PageNum - 1) * #PageSize)
IF (#OuterPageSize < 0)
SET #OuterPageSize = 0
ELSE IF (#OuterPageSize > #PageSize)
SET #OuterPageSize = #PageSize
DECLARE #sql NVARCHAR(8000)
SET #sql = 'SELECT * FROM
(
SELECT TOP ' + CAST(#OuterPageSize AS nvarchar(5)) + ' * FROM
(
SELECT TOP ' + CAST(#InnerPageSize AS nvarchar(5)) + ' * FROM <TABLE> ORDER BY <column> ASC
) AS t1 ORDER BY <column> DESC
) AS t2 ORDER BY <column> ASC'
PRINT #sql
EXECUTE sp_executesql #sql
It wasn't elegant, and it wasn't fast, but it worked.
In Oracle 12c, You may use OFFSET..FETCH..ROWS option with ORDER BY
For example, to get the 3rd record from top:
SELECT *
FROM sometable
ORDER BY column_name
OFFSET 2 ROWS FETCH NEXT 1 ROWS ONLY;
Here is a fast solution of your confusion.
SELECT * FROM table ORDER BY `id` DESC LIMIT N, 1
Here You may get Last row by Filling N=0, Second last by N=1, Fourth Last By Filling N=3 and so on.
This is very common question over the interview and this is Very simple ans of it.
Further If you want Amount, ID or some Numeric Sorting Order than u may go for CAST function in MySQL.
SELECT DISTINCT (`amount`)
FROM cart
ORDER BY CAST( `amount` AS SIGNED ) DESC
LIMIT 4 , 1
Here By filling N = 4 You will be able to get Fifth Last Record of Highest Amount from CART table. You can fit your field and table name and come up with solution.
ADD:
LIMIT n,1
That will limit the results to one result starting at result n.
Oracle:
select * from (select foo from bar order by foo) where ROWNUM = x
For example, if you want to select every 10th row in MSSQL, you can use;
SELECT * FROM (
SELECT
ROW_NUMBER() OVER (ORDER BY ColumnName1 ASC) AS rownumber, ColumnName1, ColumnName2
FROM TableName
) AS foo
WHERE rownumber % 10 = 0
Just take the MOD and change number 10 here any number you want.
For SQL Server, a generic way to go by row number is as such:
SET ROWCOUNT #row --#row = the row number you wish to work on.
For Example:
set rowcount 20 --sets row to 20th row
select meat, cheese from dbo.sandwich --select columns from table at 20th row
set rowcount 0 --sets rowcount back to all rows
This will return the 20th row's information. Be sure to put in the rowcount 0 afterward.
Here's a generic version of a sproc I recently wrote for Oracle that allows for dynamic paging/sorting - HTH
-- p_LowerBound = first row # in the returned set; if second page of 10 rows,
-- this would be 11 (-1 for unbounded/not set)
-- p_UpperBound = last row # in the returned set; if second page of 10 rows,
-- this would be 20 (-1 for unbounded/not set)
OPEN o_Cursor FOR
SELECT * FROM (
SELECT
Column1,
Column2
rownum AS rn
FROM
(
SELECT
tbl.Column1,
tbl.column2
FROM MyTable tbl
WHERE
tbl.Column1 = p_PKParam OR
tbl.Column1 = -1
ORDER BY
DECODE(p_sortOrder, 'A', DECODE(p_sortColumn, 1, Column1, 'X'),'X'),
DECODE(p_sortOrder, 'D', DECODE(p_sortColumn, 1, Column1, 'X'),'X') DESC,
DECODE(p_sortOrder, 'A', DECODE(p_sortColumn, 2, Column2, sysdate),sysdate),
DECODE(p_sortOrder, 'D', DECODE(p_sortColumn, 2, Column2, sysdate),sysdate) DESC
))
WHERE
(rn >= p_lowerBound OR p_lowerBound = -1) AND
(rn <= p_upperBound OR p_upperBound = -1);
But really, isn't all this really just parlor tricks for good database design in the first place? The few times I needed functionality like this it was for a simple one off query to make a quick report. For any real work, using tricks like these is inviting trouble. If selecting a particular row is needed then just have a column with a sequential value and be done with it.
Nothing fancy, no special functions, in case you use Caché like I do...
SELECT TOP 1 * FROM (
SELECT TOP n * FROM <table>
ORDER BY ID Desc
)
ORDER BY ID ASC
Given that you have an ID column or a datestamp column you can trust.
For SQL server, the following will return the first row from giving table.
declare #rowNumber int = 1;
select TOP(#rowNumber) * from [dbo].[someTable];
EXCEPT
select TOP(#rowNumber - 1) * from [dbo].[someTable];
You can loop through the values with something like this:
WHILE #constVar > 0
BEGIN
declare #rowNumber int = #consVar;
select TOP(#rowNumber) * from [dbo].[someTable];
EXCEPT
select TOP(#rowNumber - 1) * from [dbo].[someTable];
SET #constVar = #constVar - 1;
END;
LIMIT n,1 doesn't work in MS SQL Server. I think it's just about the only major database that doesn't support that syntax. To be fair, it isn't part of the SQL standard, although it is so widely supported that it should be. In everything except SQL server LIMIT works great. For SQL server, I haven't been able to find an elegant solution.
In Sybase SQL Anywhere:
SELECT TOP 1 START AT n * from table ORDER BY whatever
Don't forget the ORDER BY or it's meaningless.
T-SQL - Selecting N'th RecordNumber from a Table
select * from
(select row_number() over (order by Rand() desc) as Rno,* from TableName) T where T.Rno = RecordNumber
Where RecordNumber --> Record Number to Select
TableName --> To be Replaced with your Table Name
For e.g. to select 5 th record from a table Employee, your query should be
select * from
(select row_number() over (order by Rand() desc) as Rno,* from Employee) T where T.Rno = 5
SELECT
top 1 *
FROM
table_name
WHERE
column_name IN (
SELECT
top N column_name
FROM
TABLE
ORDER BY
column_name
)
ORDER BY
column_name DESC
I've written this query for finding Nth row.
Example with this query would be
SELECT
top 1 *
FROM
Employee
WHERE
emp_id IN (
SELECT
top 7 emp_id
FROM
Employee
ORDER BY
emp_id
)
ORDER BY
emp_id DESC
I'm a bit late to the party here but I have done this without the need for windowing or using
WHERE x IN (...)
SELECT TOP 1
--select the value needed from t1
[col2]
FROM
(
SELECT TOP 2 --the Nth row, alter this to taste
UE2.[col1],
UE2.[col2],
UE2.[date],
UE2.[time],
UE2.[UID]
FROM
[table1] AS UE2
WHERE
UE2.[col1] = ID --this is a subquery
AND
UE2.[col2] IS NOT NULL
ORDER BY
UE2.[date] DESC, UE2.[time] DESC --sorting by date and time newest first
) AS t1
ORDER BY t1.[date] ASC, t1.[time] ASC --this reverses the order of the sort in t1
It seems to work fairly fast although to be fair I only have around 500 rows of data
This works in MSSQL
SELECT * FROM emp a
WHERE n = (
SELECT COUNT( _rowid)
FROM emp b
WHERE a. _rowid >= b. _rowid
);
unbelievable that you can find a SQL engine executing this one ...
WITH sentence AS
(SELECT
stuff,
row = ROW_NUMBER() OVER (ORDER BY Id)
FROM
SentenceType
)
SELECT
sen.stuff
FROM sentence sen
WHERE sen.row = (ABS(CHECKSUM(NEWID())) % 100) + 1
select * from
(select * from ordered order by order_id limit 100) x order by
x.order_id desc limit 1;
First select top 100 rows by ordering in ascending and then select last row by ordering in descending and limit to 1. However this is a very expensive statement as it access the data twice.
It seems to me that, to be efficient, you need to 1) generate a random number between 0 and one less than the number of database records, and 2) be able to select the row at that position. Unfortunately, different databases have different random number generators and different ways to select a row at a position in a result set - usually you specify how many rows to skip and how many rows you want, but it's done differently for different databases. Here is something that works for me in SQLite:
select *
from Table
limit abs(random()) % (select count(*) from Words), 1;
It does depend on being able to use a subquery in the limit clause (which in SQLite is LIMIT <recs to skip>,<recs to take>) Selecting the number of records in a table should be particularly efficient, being part of the database's meta data, but that depends on the database's implementation. Also, I don't know if the query will actually build the result set before retrieving the Nth record, but I would hope that it doesn't need to. Note that I'm not specifying an "order by" clause. It might be better to "order by" something like the primary key, which will have an index - getting the Nth record from an index might be faster if the database can't get the Nth record from the database itself without building the result set.
Most suitable answer I have seen on this article for sql server
WITH myTableWithRows AS (
SELECT (ROW_NUMBER() OVER (ORDER BY myTable.SomeField)) as row,*
FROM myTable)
SELECT * FROM myTableWithRows WHERE row = 3
I have a query with many wheres and orders criterias. One of the fields of the select is 'price' (element price) but I would like to have also (in every row) the maximun price of all the selected elements.
I tried to include MAX aggregate function on select hoping that this will return desired value, but insetead of that, price and MAX(price) returns the same. Searching into MySql doc I found the reason:
If you use a group function in a
statement containing no GROUP BY
clause, it is equivalent to grouping
on all rows.
Is there a way to solve this problem?
Thanks in advance!
There's a similar question (but not resolving this): find max value without aggregate operator in mysql
You can do this:
SELECT
id,
price,
(SELECT MAX(price) FROM your_table) AS max_price
FROM your_table
I'm not sure why you'd want to return that value on every row though... I'd probably do this in two separate queries, or else use a UNION ALL:
SELECT id, price FROM your_table
UNION ALL
SELECT NULL, MAX(price) FROM your_table
Maybe you could use a stored procedure like so:
CREATE PROCEDURE QueryWithMax ([parameter list if necessary])
BEGIN
-- Obtain the maximum price
DECLARE x INT UNSIGNED; -- change datatype if appropriate
SET x = SELECT
MAX(price)
FROM
...
WHERE
...
;
-- Now do your query
SELECT
price,
[other columns],
x AS MaxPrice
FROM
...
WHERE
...
GROUP BY
...
;
END
I haven't tried this, but if you had a subquery that extracts the maximum price (so you get one row), and then do a cross join (cartesian product) with it. You should get something like what you want. I can't vouch for how fast this would be.