Select Random value from columns

Question

I want to cleanse data on the postcode column.

So far I have

declare @postcode table
(
letter1 varchar(4)
,number1 varchar(4)
,number2 varchar(4)
,letter3 varchar(4)
)

insert into @postcode values
('a','1','1','a'),
('b','2','2','b'),
('c','3','3','c')

All the way down the alphabet to

(null,'37','37',null)

My problem is that I need to select a random letter, number then letter so the postcode turns up looking something like

d12 4RF

The rest of my code is below:

declare @postcodemixup table
                      (ID int identity(1,1)
                       ,Postcode varchar(20))

declare @rand varchar(33)

/*pick a random row and mash it up */
declare @realpostcode varchar (30)

select @realpostcode = letter1 + '' +number1 + ' ' + number1 + '' + letter2 
from @postcode 
where letter1 = 'a'

select @realpostcode

insert into @postcodemixup values(@realpostcode), (@realpostcode)

select * from @postcodemixup

Any answers, reading material or suggests would be great.

Thank you,

Jay

Answer 1

Some things that may help:

To get a random integer between 1 and 37: CONVERT(int, RAND() * 37) + 1

To get a random letter: CHAR((RAND() * 26) + ASCII('A'))

If you want a random row, you could try this, though it wouldn't be particularly speedy:

declare @rowCount int
    ,   @randomRow int

select @rowCount = COUNT(*) FROM Table1
select @randomRow = RAND() * @rowCount + 1

With A
as  (
  select Table1.*
      ,  rownumber = ROW_NUMBER() OVER (Order BY ID) -- order by something, doesn't matter what
  from   Table1
)
select * 
from   A 
where  rownumber = @randomRow

Answer 2

Not sure this is exactly what you need, but assuming the formula needed is "letter-digit-digit-space-digit-letter-letter" (according to picture), data can be generated eg with the following statement:

;with
    A as (select cast(char((rand(checksum(newid())) * 26) + ascii('A')) as varchar(10)) A),
    D as (select cast(cast(rand(checksum(newid())) * 10 as int) as varchar(10)) D)
select top (10000)
    row_number() over (order by @@spid) as id,
    A1.A + D1.D + D2.D + ' ' + D3.D + A2.A + A3.A as postcode
from sys.all_columns c1, sys.all_columns c2,
    A A1, D D1, D D2, D D3, A A2, A A3

Answer 3

If your random postcode must be based values, predefined in the @postcode table, try this query:

set @realpostcode = (select top 1 letter1 from @postcode order by NEWID()) + 
                (select top 1 number1 from @postcode order by NEWID()) +
                (select top 1 number2 from @postcode order by NEWID()) +
                (select top 1 letter2 from @postcode order by NEWID())