SQL remove unwanted special characters from a string - sql

Question

Hi i am new to SQL and am writing a case statement for a column of grade values.
The values can be a length of 3 like A02, B04, A10, A09, D03. The first character is a letter while the next 2 are digits.
If a user enters in 'A02 I want to change it to do A02. Basically remove any special characters if there are present.
CASE
WHEN Grade like '[^0-9A-z]%' THEN ''
else Grade end as Grade
So far I have this but I am not sure how to use regex to remove the character only search for it.

Answer 1

Unless you really want to do a CASE for the fun of it, in oracle I'd do it like this which removes punctuation characters and spaces when you select it. Note this does not verify format so a grade of Z1234 would get returned.
WITH tbl(ID, grade) AS (
SELECT 1, 'A01' FROM dual UNION ALL
SELECT 1, '''B02' FROM dual UNION ALL
SELECT 2, '$ C01&' FROM dual
)
SELECT ID, grade, REGEXP_REPLACE(grade, '([[:punct:]]| )') AS grade_scrubbed
from tbl;
ID GRADE GRADE_SCRUBBED
---------- --------- --------------
1 A01 A01
1 'B02 B02
2 $ C01& C01
3 rows selected.
HOWEVER, that said, since you seem to want to verify the format and use regex, you could do it this way although it's a little fugly. See comments.
WITH tbl(ID, grade) AS (
-- Test data. Include every crazy combo you'd never expect to see,
-- because you WILL see it, it's just a matter of time :-)
SELECT 1, 'A01' FROM dual UNION ALL
SELECT 1, '''B02' FROM dual UNION ALL
SELECT 2, '$ C01&' FROM dual UNION ALL
SELECT 3, 'DDD' FROM dual UNION ALL
SELECT 4, 'A'||CHR(10)||'DEF' FROM dual UNION ALL
SELECT 5, 'Z1234' FROM dual UNION ALL
SELECT 6, NULL FROM dual
)
SELECT ID, grade,
CASE
-- Correct format of A99.
WHEN REGEXP_LIKE(grade, '^[A-Z]\d{2}$')
THEN grade
-- if not A99, see if stripping out punctuation and spaces make it match A99.
-- If so, return with punctuation and spaces stripped out.
WHEN NOT REGEXP_LIKE(grade, '^[A-Z]\d{2}$')
AND REGEXP_LIKE(REGEXP_REPLACE(grade, '([[:punct:]]| )'), '^[A-Z]\d{2}$')
THEN REGEXP_REPLACE(grade, '([[:punct:]]| )')
-- if not A99, and stripping out punctuation and spaces didn't make it match A99,
-- then the grade is in the wrong format.
WHEN NOT REGEXP_LIKE(grade, '^[A-Z]\d{2}$')
AND NOT REGEXP_LIKE(REGEXP_REPLACE(grade, '([[:punct:]]| )'), '^[A-Z]\d{2}$')
THEN 'Invalid grade format'
-- Something fell through all cases we tested for. Always expect the unexpected!
ELSE 'No case matched!'
END AS grade_scrubbed
from tbl;
ID GRADE GRADE_SCRUBBED
---------- -------------------- --------------------
1 A01 A01
1 'B02 B02
2 $ C01& C01
3 DDD Invalid grade format
4 A
DEF Invalid grade format
5 Z1234 Invalid grade format
6 No case matched!
7 rows selected.