T-SQL RegExp to find sequential repeated characters - regex

Question

I'm looking for a RegExp to find duplicated characters in a entire word in SQL Server and Regular Expressions (RegExp). For Example:
"AAUGUST" match (AA)
"ANDREA" don't match (are 2 vowels "A", buit are separated)
"ELEEPHANT" match (EE)
I was trying with:
SELECT field1
FROM exampleTable
WHERE field1 like '%([A-Z]){2}%'
But it doesn't work.
I apreciated for your help.
Thanks!

Answer 1

You can't do what you're asking with T-SQL's LIKE.
Your best bet is to look at using the Common Language Runtime (CLR), but it can also be achieved (albeit painfully slowly) using, for example, a scalar value function as follows:
create function dbo.ContainsRepeatingAlphaChars(#str nvarchar(max)) returns bit
as begin
declare #p int, -- the position we're looking at
#c char(1) -- the previous char
if #str is null or len(#str) < 2 return 0;
select #c = substring(#str, 1, 1), #p = 1;
while (1=1) begin
set #p = #p + 1; -- move position pointer ahead
if #p > len(#str) return 0; -- if we're at the end of the string and haven't already exited, we haven't found a match
if #c like '[A-Z]' and #c = substring(#str, #p, 1) return 1; -- if last char is A-Z and matches the current char then return "found!"
set #c = substring(#str, #p, 1); -- Get next char
end
return 0; -- this will never be hit but stops SQL Server complaining that not all paths return a value
end
GO
-- Example usage:
SELECT field1
FROM exampleTable
WHERE dbo.ContainsRepeatingAlphaChars(field1) = 1
Did I mention that it would be slow? Don't use this on a large table. Go CLR.