Generating Test Data with SQL Scripts

<<< These scripts were tested on MS SQL Server  2019 >>>

From time to time we need to generate huge data for testing. Without any data generating tool we can achieve it by using some SQL Scripts. these scripts are different from regular query scripts.

Generate list of data

CREATE TABLE #accounts ( fname VARCHAR(20), lname VARCHAR(20))
GO
INSERT #accounts VALUES ('Fred', 'Flintstone')
GO 1000

SELECT TOP 10 * FROM #accounts

fname lname
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone
Fred  Flintstone

ALTER TABLE #accounts ADD id INT IDENTITY(1,1)
SELECT TOP 10 * FROM #accounts
GO

fname lname      id
Fred  Flintstone 1
Fred  Flintstone 2
Fred  Flintstone 3
Fred  Flintstone 4
Fred  Flintstone 5
Fred  Flintstone 6
Fred  Flintstone 7
Fred  Flintstone 8
Fred  Flintstone 9
Fred  Flintstone 10

ALTER TABLE #accounts ADD id INT

DECLARE @id INT
SET @id = 0
UPDATE #accounts
SET @id = id = @id + 1
OPTION ( MAXDOP 1 )
GO

SELECT * FROM #accounts
GO

fname lname      id
Fred  Flintstone 1
Fred  Flintstone 2
Fred  Flintstone 3
Fred  Flintstone 4
Fred  Flintstone 5
Fred  Flintstone 6
Fred  Flintstone 7
Fred  Flintstone 8
Fred  Flintstone 9
Fred  Flintstone 10

Note: MAXDOP is max degree of parallelism, set it to 1 to avoid duplicate value if running on multiple processors machine. Read article 1 for detail.

Generate sequence numbers

Using sys.all_columns table

SELECT TOP (1000) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM sys.all_columns

Generate huge Rows using CROSS JOIN

SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL))
FROM sys.all_columns ac1
CROSS JOIN sys.all_columns ac2

Note: the number of rows being generated are depending on the sys.all_columns table size. It took 1 minute to generate 30 million rows in my machine. You could use top n to limit the number of rows being generated.

Direct generation

SELECT n FROM (VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) v(n) 
select * from x

WITH x AS (SELECT n FROM (VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) v(n))
SELECT ones.n + 10*tens.n + 100*hundreds.n + 1000*thousands.n
FROM x ones, x tens, x hundreds, x thousands
ORDER BY 1

SELECT ones.n + 10*tens.n + 100*hundreds.n + 1000*thousands.n
FROM (VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) ones(n),
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) tens(n),
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) hundreds(n),
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) thousands(n)
WHERE ones.n + 10*tens.n + 100*hundreds.n + 1000*thousands.n BETWEEN 1000 AND 2000
ORDER BY 1

DECLARE @startnum INT=1000, @endnum INT=1050
;
WITH gen AS (
SELECT @startnum AS num
UNION ALL
SELECT num+1 FROM gen WHERE num+1<=@endnum
)
SELECT * FROM gen
option (maxrecursion 10000)

Generate random numbers

IF OBJECT_ID('tempdb..#SomeTestTable','U') IS NOT NULL DROP TABLE #SomeTestTable

DECLARE @NumberOfRows INT = 1000000,
        @StartValue   INT = 400,
        @EndValue     INT = 500
DECLARE @Range        INT = @EndValue - @StartValue + 1;
SELECT TOP (@NumberOfRows)
        SomeRandomInteger =  ABS(CHECKSUM(NEWID())) % @Range + @StartValue,
        SomeRandomFloat   = RAND(CHECKSUM(NEWID())) * @Range + @StartValue
INTO #SomeTestTable
FROM sys.all_columns ac1
CROSS JOIN sys.all_columns ac2

select * from #SomeTestTable order by 1

Summary

We could use system table to generate huge number of custom data by using CROSS JOIN on system tables. We also can generate huge number of random data by just using a formula. To limit the number of data being generated we can use SELECT TOP clause.

By the way, "Tally" table is another good way to generate data, more detail read this article: The "Numbers" or "Tally" Table: What it is and how it replaces a loop

Reference

1. Populate a SQL Server column with a sequential number not using an identity
2. What MAXDOP setting should be used for SQL Server
3. How to generate a range of numbers between two numbers?

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Author: IT Team