Some of the examples were taken from this SOen response from @ YaakovEllis

  

I've already warned you that this has not been done performance testing, which can probably be a bit tricky if you need to check out many things. I want to run my own tests and maybe suggest different ways.

     

Another detail, the use of LIMIT , TOP 1 , rownum , etc is only to indicate that there was limitation of results, after all the intention is to get random results and not only to order in a random fashion

MySQL

Select random MySQL:

SELECT column FROM table
ORDER BY RAND()
LIMIT 1

PostgreSQL

Select random in PostgreSQL:

SELECT column FROM table
ORDER BY RANDOM()
LIMIT 1

SQL Server

Select random in Microsoft SQL Server:

SELECT TOP 1 column FROM table
ORDER BY NEWID()

IBM DB2

Select random in IBM DB2

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

Oracle

Select Random in Oracle:

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

SQLite

Select random in Sqlite:

SELECT column FROM table
ORDER BY RANDOM() LIMIT 1

In SQL Server, if you do not need to select all rows and only a sample rows and performance is important, use the following:

SELECT * FROM table
  WHERE (ABS(CAST(
  (BINARY_CHECKSUM(*) *
  RAND()) as int)) % 100) < 10

The idea here is to generate a random number between 0 and 99 and then select all that are smaller than 10. That way selecting ~ 10% of the base. You can change the 100 of the query by another value if you need to pick up portions smaller than 1% of the base.