I see there is still no answer that has been chosen as the best. Besides the solutions already mentioned in this thread, I can suggest using ApexSQL Generate – a SQL data generator tool , which has the ability to quickly generate millions of rows, using various data sources, with a variety of data generators.

It features a fully functional free trial, so you can download it and test to see if it will get your job done.

For mysql databases you can use filldb.info .

It automatically generate data and fill your database tables with this dummy data

In case someone is looking for a simple way to do this without extra software.

We just need a function that returns a random number:

-- Create the RANDBETWEEN function
-- Usage: SELECT dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID())))
CREATE FUNCTION dbo.RANDBETWEEN(@minval TINYINT, @maxval TINYINT, @random NUMERIC(18,10))
RETURNS TINYINT
AS
BEGIN
  RETURN (SELECT CAST(((@maxval + 1) - @minval) * @random + @minval AS TINYINT))
END
GO

And then you can run a query like this:

-- Insert 1 million records into the Person table
INSERT INTO Person (FirstName,LastName,CityId)
SELECT TOP 1000000
    CASE
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 0 THEN 'John'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 1 THEN 'Jack'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 2 THEN 'Bill'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 3 THEN 'Mary'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 4 THEN 'Kate'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 5 THEN 'Matt'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 6 THEN 'Rachel'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 7 THEN 'Tom'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 8 THEN 'Ann'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 9 THEN 'Andrew'
    ELSE 'Bob' END AS FirstName,
    CASE
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 0 THEN 'Smith'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 1 THEN 'Morgan'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 2 THEN 'Simpson'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 3 THEN 'Walker'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 4 THEN 'Bauer'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 5 THEN 'Taylor'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 6 THEN 'Morris'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 7 THEN 'Elliot'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 8 THEN 'White'
        WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 9 THEN 'Davis'
    ELSE 'Brown' END AS LastName,
    dbo.RANDBETWEEN(1,15,RAND(CHECKSUM(NEWID()))) as CityId
FROM sys.all_objects a
CROSS JOIN sys.all_objects b
GO

Result:

Adjust the query accordingly to match your table/column names.

the very simple SQL I use generally :

create table fillTbl (msg nvarchar(255))
insert into fillTbl select top 4285 description from sys.sysmessages where msglangid=1033 -- ~ 1 Mo
GO 100 -- the number of Mo you want to add
exec sp_spaceused 'fillTbl' -- space in the table
exec sp_spaceused -- space in the database
-- drop table fillTbl -- reset the space added