select several lines randomly according to several categories

Question

select several lines randomly according to several categories

abdalah.mehdoini

SSC Eights!

Points: 976
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September 16, 2019 at 1:33 pm

#3680324

Hello,
I have the following dataset:
Family Room subfamily
1 5 6
2 5 7
3 5 7
4 2 3
I would like to extract the data from this table randomly. It would take in the extraction a piece taken at random by couple family / sub-family.
For this dataset for example the extraction would be:
Family Room subfamily
1 5 6
3 5 7
4 2 3
I do not know how to attack the request to have the expected result ... If someone has clues I am a taker.
Thanks in advance.

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Alan Burstein SSC Guru Points: 61136 More actions · Answer 1

You can use TOP and ORDER BY NEWID() like this:

-- Sample data
DECLARE @yourdata TABLE 
(
Family INT,
Room INT,
subfamily INT
);
INSERT @yourdata VALUES (1,5,6),(2,5,7),(3,5,7),(4,2,3),(4,2,4);

-- Number of Rows 
DECLARE @rows INT = 3;

SELECT TOP (@rows) y.Family, y.Room, y.subfamily
FROM @yourdata AS y
ORDER BY NEWID();

You can return a random number of rows using CHECKSUM and NEWID like this:

DECLARE @yourdata TABLE 
(
Family INT,
Room INT,
subfamily INT
);
INSERT @yourdata VALUES (1,5,6),(2,5,7),(3,5,7),(4,2,3),(4,2,4);

-- number of rows to return (e.g. 2 to 4 rows)
DECLARE @low INT = 2, @high INT = 4;

SELECT TOP (ABS(CHECKSUM(NEWID())%(@high-@low+1))+@low) y.Family, y.Room, y.subfamily
FROM @yourdata AS y
ORDER BY NEWID();

"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."

-- Itzik Ben-Gan 2001

jcelko212 32090 SSCrazy Eights Points: 9220 More actions · Answer 2

>> I have the following dataset: <<

And thanks to your lack of netiquette, we have no DDL. When you're at work do you ask other people to do the basic things that an SQL programmer should do because you can't do them yourself? we have no datatypes, no keys no constraints. And even column names are vague.

>> I would like to extract the data from this table randomly. It would take in the extraction a piece taken at random by couple family / sub-family. I do not know how to attack the request to have the expected result ... If someone has clues I am a taker. <<

What sampling method do you want to use? Random? Stratified? SQL was not meant for this and the attempts to paste it into SQL have been disappointing. How big a sample do you want to get from your population? To do this right, you're going to have to know some basic statistics and it doesn't sound like you do.

You might want to look at an old, but still, a very good introductory book entitled "A Sampler on Sampling" by Bill Williams (ISBN 0471030368).

Please post DDL and follow ANSI/ISO standards when asking for help.

Alan Burstein SSC Guru Points: 61136 More actions · Answer 3

And thanks to your lack of netiquette, we have no DDL.

I think what I posted should answer the OP's question as well as yours Joe.

"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."

-- Itzik Ben-Gan 2001

jcelko212 32090 SSCrazy Eights Points: 9220 More actions · Answer 4

> You can return a random number of rows using CHECKSUM and NEWID <<

Is this method a uniform random thing? I think I remember that a lot of these SQL Server trick skew toward the rows that are at the front of a data page ...

Please post DDL and follow ANSI/ISO standards when asking for help.

rVadim Hall of Fame Points: 3969 More actions · Answer 5

Why not use TABLESAMPLE?

SELECT * FROM YourTable TABLESAMPLE(100 ROWS)
SELECT * FROM YourTable TABLESAMPLE(10 PERCENT)

--Vadim R.

Sumathi Valued Member Points: 61 More actions · Answer 6

This can be done using

SELECT TOP (@rows) y.Family, y.Room, y.subfamily

FROM @Table AS y

ORDER BY NEWID();

OR

SELECT y.Family, y.Room, y.subfamily

FROM @Table AS y TABLESAMPLE(3 ROWS)

But, the TABLESAMPLE clause cannot be applied to derived tables, tables from linked servers, tables derived from table-valued functions, rowset functions or OPENXML or from views.