A more controllable random string generator function for SQL Server, Sql Server

A more controllable random string generator function for SQL Server

How to generate random strings on SQL Server, 
While controling their length and the type of chars they can contain.

Published on What the # do I know.

https://zoharpeled.wordpress.com/2019/12/10/a-more-controllable-random-string-generator-function-for-sql-server/

CREATE VIEW dbo.GuidGenerator
AS
    SELECT Newid() As NewGuid;
GO

CREATE FUNCTION dbo.RandomStringGenerator
(
    -- the minimum length 
    @MinLength int, 
    -- the maximum length
    @MaxLength int, 
    -- the maximum number of rows to return. Note: up to 1,000,000 rows
    @Count int, 
    -- 1, 2 and 4 stands for lower-case, upper-case and digits. 
    -- a bitwise combination of these values can be used to generate all possible combinations:
    -- 3: lower and upper, 5: lower and digis, 6: upper and digits, 7: lower, upper nad digits
    @CharType tinyint 
)
RETURNS TABLE
AS 
RETURN 
-- An inline tally table with 1,000,000 rows
WITH E1(N) AS (SELECT N FROM (VALUES (1), (2), (3), (4), (5), (6), (7), (8), (9), (10)) V(N)),   -- 10
     E2(N) AS (SELECT 1 FROM E1 a, E1 b), --100
     E3(N) AS (SELECT 1 FROM E2 a, E2 b), --10,000
     Tally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY @@SPID) FROM E3 a, E2 b) --1,000,000

SELECT TOP(@Count) 
        n As Number, 
        (
        SELECT  TOP (Length) 
                -- choose what char combination to use for the random part
                CASE @CharType 
                    WHEN 1 THEN Lower
                    WHEN 2 THEN Upper
                    WHEN 3 THEN IIF(Rnd % 2 = 0, Lower, Upper)
                    WHEN 4 THEN Digit
                    WHEN 5 THEN IIF(Rnd % 2 = 0, Lower, Digit)
                    WHEN 6 THEN IIF(Rnd % 2 = 0, Upper, Digit)
                    WHEN 7 THEN 
                        CASE Rnd % 3
                            WHEN 0 THEN Lower
                            WHEN 1 THEN Upper
                            ELSE Digit
                        END
                END
        FROM Tally As t0  
        -- create a random number from a guid using the GuidGenerator view
        CROSS APPLY (SELECT Abs(Checksum(NewGuid)) As Rnd FROM GuidGenerator) As rand
        CROSS APPLY
        (
            -- generate a random lower-case char, upper-case char and digit
            SELECT  CHAR(97 + Rnd % 26) As Lower, -- Random lower case letter
                    CHAR(65 + Rnd % 26) As Upper,-- Random upper case letter
                    CHAR(48 + Rnd % 10) As Digit -- Random digit
        ) As Chars
        WHERE  t0.n <> -t1.n -- Needed for the subquery to get re-evaluated for each row
        FOR XML PATH('') 
        ) As RandomString
FROM Tally As t1
CROSS APPLY
(
    -- Select a random length between @MinLength and @MaxLength (inclusive)
    SELECT TOP 1 n As Length
    FROM Tally As t2
    CROSS JOIN GuidGenerator 
    WHERE t2.n >= @MinLength
    AND t2.n <= @MaxLength
    AND t2.n <> t1.n
    ORDER BY NewGuid
) As Lengths;

DECLARE @Count int = 10;

SELECT  CAST(IntVal.RandomString As Int) As IntValue, 
        UpVal.RandomString as UpperCaseValue, 
        LowVal.RandomString as LowerCaseValue, 
        MixVal.RandomString as MixedValue
FROM dbo.RandomStringGenerator(3, 7, @Count, 4) As IntVal
JOIN dbo.RandomStringGenerator(10, 10, @Count, 1) As LowVal
    ON IntVal.Number = LowVal.Number
JOIN dbo.RandomStringGenerator(5, 10, @Count, 2) As UpVal
    ON IntVal.Number = UpVal.Number
JOIN dbo.RandomStringGenerator(10, 20, @Count, 7) As MixVal
    ON IntVal.Number = MixVal.Number


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