How to request a random row in SQL?

Question

How can I request a random row (or as close to truly random as is possible) in pure SQL?

Answer 1

See this post: SQL to Select a random row from a database table. It goes through methods for doing this in MySQL, PostgreSQL, Microsoft SQL Server, IBM DB2 and Oracle (the following is copied from that link):

Select a random row with MySQL:

SELECT column FROM table
ORDER BY RAND()
LIMIT 1

Select a random row with PostgreSQL:

SELECT column FROM table
ORDER BY RANDOM()
LIMIT 1

Select a random row with Microsoft SQL Server:

SELECT TOP 1 column FROM table
ORDER BY NEWID()

Select a random row with IBM DB2

SELECT column, RAND() as IDX 
FROM table 
ORDER BY IDX FETCH FIRST 1 ROWS ONLY

Select a random record with Oracle:

SELECT column FROM
( SELECT column FROM table
ORDER BY dbms_random.value )
WHERE rownum = 1

Answer 2

In SQL Server you can combine TABLESAMPLE with NEWID() to get pretty good randomness and still have speed. This is especially useful if you really only want 1, or a small number, of rows.

SELECT TOP 1 * FROM [table] 
TABLESAMPLE (500 ROWS) 
ORDER BY NEWID()

Answer 3

 SELECT * FROM table ORDER BY RAND() LIMIT 1

Answer 4

You didn't say which server you're using. In older versions of SQL Server, you can use this:

select top 1 * from mytable order by newid()

In SQL Server 2005 and up, you can use TABLESAMPLE to get a random sample that's repeatable:

SELECT FirstName, LastName
FROM Contact 
TABLESAMPLE (1 ROWS) ;

Answer 5

For SQL Server 2005 and above, extending @GreyPanther's answer for the cases when num_value has not continuous values. This works too for cases when we have not evenly distributed datasets and when num_value is not a number but a unique identifier.

WITH CTE_Table (SelRow, num_value) 
AS 
(
    SELECT ROW_NUMBER() OVER(ORDER BY ID) AS SelRow, num_value FROM table
) 

SELECT * FROM table Where num_value = ( 
    SELECT TOP 1 num_value FROM CTE_Table  WHERE SelRow >= RAND() * (SELECT MAX(SelRow) FROM CTE_Table)
)

Answer 6

For SQL Server 2005 and 2008, if we want a random sample of individual rows (from Books Online):

SELECT * FROM Sales.SalesOrderDetail
WHERE 0.01 >= CAST(CHECKSUM(NEWID(), SalesOrderID) & 0x7fffffff AS float)
/ CAST (0x7fffffff AS int)