Hi Rudy. Is there a way to get a random (and not sequential) of X rows (with all data) in one query (and not X...
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.
Short answer: No.
Long answer: Yes, sort of, but you might not like it.
There is no way in standard SQL to select rows randomly. Some sort of programming is required.
Let's say you have a table with many rows and the primary key is an integer, like an autonumber or identity key or sequence number. If you can generate random keys from the range of primary keys in use, these may be used to select rows.
First, you need a "driver" table which will hold the generated keys --
create table Driver ( driverID autonumber , randno integer)
Next, find the range of primary keys in use --
select min(primaryID) as MinID , max(primaryID) as MaxID from yourTable
Now, generate some random keys using the min and max ID values as the range bounds (note: the following is pseudocode, not any specific programming language) and insert them into the driver table --
for 1 <= j <= 100 r = random(minID, maxID) insert into Driver(randno) values (r) end
Finally, run your select using the driver table of random keys --
select yourTable.* from Driver, yourTable where yourTable.ID = (select min(primaryID) from yourTable where primaryID >= Driver.randno)
Ugly, to say the least. And only pseudorandom. And not tested lately. Note the subquery is required in case there are gaps in the actual primary keys in yourTable.
Another way is to arbitrarily take a substring out of a string conversion of some convenient column in yourTable like a timestamp --
select TOP 100 yourtable.* , substring(cast(yourTimestamp as char(20)) from 14 to 18) as foo from yourTable order by foo desc
But that's even less random.
The best solution, for situations where you only need a small number of rows, such as in testing, is to have a sample table which contains not random rows of live data, but test cases -- in other words, a place where you can collect those rows which are of interest or which represent conditions you want to test for.
For More Information
- What do you think about this answer? E-mail us at editor@searchDatabase.com with your feedback.
- The Best Microsoft SQL Server Web Links: tips, tutorials, scripts, and more.
- The Best SQL Web Links
- Have a SQL tip to offer your fellow DBA's and developers? The best tips submitted will receive a cool prize--submit your tip today!
- Ask your technical SQL questions--or help out your peers by answering them--in our live discussion forums.
- Ask the Experts yourself: Our SQL guru is waiting to answer your technical questions.
Dig Deeper on Oracle and SQL
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.