SQL Server Random Number

Greetings Dev, whether you are a beginner or experienced SQL Server user, you may have encountered situations where you need to generate random numbers in your queries. In this article, we will explore the different ways of generating random numbers in SQL Server and their practical applications.

What is a Random Number?

A random number is a value that is unpredictable and appears to be chosen by chance. Random numbers are used in various applications such as encryption, statistical analysis, and gaming.

What is Pseudo-Random Number?

A pseudo-random number is a sequence of numbers that appears to be random but is generated using a deterministic algorithm. In other words, the same sequence of pseudo-random numbers can be generated again if the same algorithm and seed value are used.

Generating Random Numbers in SQL Server

SQL Server provides several methods to generate random numbers. The following are the most common ways:

Using RAND() Function

The RAND() function is a built-in function in SQL Server that generates a pseudo-random float value between 0 and 1. We can use this function to generate a random number within a specific range.

For example, the following query generates a random number between 1 and 10:

Query
Result
SELECT (RAND() * 10) + 1 AS RandomNumber
RandomNumber
————
5.39593825

In this query, we multiply the RAND() function by 10 to get a value between 0 and 10, and then add 1 to shift the range to 1 to 10.

Using NEWID() Function

The NEWID() function is a built-in function in SQL Server that generates a unique GUID (Global Unique Identifier) value. We can use this function to generate a random number by converting the GUID value to an integer or bigint data type.

For example, the following query generates a random number between 1 and 10:

Query
Result
SELECT ABS(CONVERT(BIGINT,CONVERT(VARBINARY(6),NEWID()))) % 10 + 1 AS RandomNumber
RandomNumber
————
7

In this query, we convert the NEWID() value to binary, then to bigint, and then take the absolute value of the remainder of dividing it by 10, and finally, add 1 to shift the range to 1 to 10. The conversion to binary and bigint is necessary because the remainder operator is not defined for uniqueidentifier data type.

Using CHECKSUM(NEWID()) Function

The CHECKSUM() function is a built-in function in SQL Server that generates a hash value for a given expression. We can use this function in combination with the NEWID() function to generate a random number.

For example, the following query generates a random number between 1 and 10:

Query
Result
SELECT ABS(CHECKSUM(NEWID())) % 10 + 1 AS RandomNumber
RandomNumber
————
4

In this query, we use the NEWID() function to generate a unique value for each row, and then use the CHECKSUM() function to generate a hash value for that value. The ABS() function is used to get the absolute value of the hash value, and then the remainder of dividing it by 10 is taken, and finally, 1 is added to shift the range to 1 to 10.

Practical Applications of Random Numbers in SQL Server

Random numbers can be used in various ways in SQL Server. The following are some practical applications:

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Sampling Data

Random numbers can be used to sample data from a large table. For example, if we have a table with millions of rows, we can use a random number to select a subset of rows for analysis.

Shuffling Data

Random numbers can be used to shuffle the order of rows in a table. For example, if we have a table with sequential IDs, we can use a random number to sort the rows randomly.

Generating Test Data

Random numbers can be used to generate test data for unit testing or performance testing. For example, if we need to test the behavior of a query with different input values, we can generate random numbers for the input parameters.

FAQ

Can RAND() function be used to generate integers?

No, the RAND() function generates float values between 0 and 1. To generate integers, we need to use some arithmetic operations such as multiplication, addition, and rounding.

Is it possible to generate truly random numbers in SQL Server?

No, it is not possible to generate truly random numbers using deterministic algorithms. Truly random numbers require a source of entropy, such as radioactive decay or atmospheric noise.

Which method is the best for generating random numbers in SQL Server?

It depends on the specific requirements of your application. If you need a simple and fast way to generate random numbers, the RAND() function may be sufficient. If you need a more complex and diverse distribution of numbers, the NEWID() or CHECKSUM(NEWID()) method may be more suitable.

Can random numbers be used for encryption?

No, random numbers alone cannot be used for encryption. Encryption requires a secure key and an algorithm that uses the key to transform the data. Random numbers can be used to generate keys or initialization vectors for encryption, but they cannot be used directly for encryption.