Question

I’d like to run a query which for a given field will count the instances of a particular character.

For example if I had a table called ‘Friends’ with a ‘Names’ field containing rows: Edward, James, Mike. I’d get the output:

A 2,
D 2,
E 3,
I 1,
and so on…

Answer 1

The generic answer is that you need to split each name into a table of constituent characters, then count those.

You don’t mention which RDBMS you’re using. The answer varies a bit by database engine.

For example, this will work on SQL 2005+:

DECLARE @friends TABLE (NAMES VARCHAR(30))
DECLARE @maxLen INT

INSERT @friends (NAMES)
SELECT 'Edward'
UNION SELECT 'James'
UNION SELECT 'Mike'

SELECT @maxLen = MAX(LEN(NAMES)) FROM @friends

;WITH numsCte 
AS 
( 
        --dynamic numbers table. If you have a numbers table in your database
        --use that instead, as it will be more efficient.
        SELECT 1 AS n 
        UNION ALL 
        SELECT n+1 FROM numsCte 
        WHERE n < @maxLen
)
,charCTE
AS
( 
        --split the string into a dataset
        SELECT *
        FROM numsCte AS nm
        CROSS APPLY (SELECT NAMES, SUBSTRING(NAMES, n, 1) AS splitChar 
                     FROM @friends
                    ) AS st
        WHERE splitChar > ''
)
SELECT  UPPER(splitChar) AS letter
        ,COUNT(1) AS cnt
FROM charCTE
GROUP BY splitChar
ORDER BY splitChar

But almost certainly won’t work on any other database engines.