sqlite advanced case sensitive query - sqlite

Question

i search for a special kind of query in SQLite
to sort a notes table.
The result from the query should be like this:
id oid
1 1
2 1,1
5 1,1,a
6 1,1,a,1
3 1,1,A
4 1,1,A,1
But with the folling code I receive this:
CREATE TABLE note (
id INTEGER PRIMARY KEY AUTOINCREMENT,
created DATETIME DEFAULT CURRENT_TIMESTAMP,
oid VARCHAR unique,
tit VARCHAR,
dsc VARCHAR
);
select id, oid from note
order by oid collate NOCASE
Result:
id oid
1 1
2 1,1
5 1,1,a
3 1,1,A
6 1,1,a,1
4 1,1,A,1
Any suggestions?
Thanks
--jonah

Answer 1

The following transforms the sort keys so that the normal case sensitive ordering yields the requested result:
If there was a togglecase() function, the function would uppercase lowercase and lowercase uppercase (for example Hello => hELLO), one could ORDER BY togglecase(oid) and the result would be in the order requested.
You could define such a function and expose it to SQLite as a UDF. It could also be possible to write this function using builtin SQLite functions but I don't know them well enough to give an answer using them. The following is an example of such a function in Python:
def togglecase(s):
def toggle(l):
if l.isupper():
return l.lower()
if l.islower():
return l.upper()
return l
return ''.join(toggle(l)
for l in s)
Note that for proper Unicode support it needs to iterate over graphemes. Not over code points.
See that this does what I described it to do:
>>> togglecase("1,1,A")
'1,1,a'
>>> togglecase("1,1,a")
'1,1,A'
It is possible to test if this sorts correctly in Python:
>>> sorted(["1", "1,1", "1,1,a", "1,1,a,1", "1,1,A", "1,1,A,1"])
['1', '1,1', '1,1,A', '1,1,A,1', '1,1,a', '1,1,a,1']
See how the uppercase follows the lowercase:
>> sorted(["1", "1,1", "1,1,a", "1,1,a,1", "1,1,A", "1,1,A,1"], key=togglecase)
['1', '1,1', '1,1,a', '1,1,a,1', '1,1,A', '1,1,A,1']
Now if you use it in SQLite like:
SELECT id, oid
FROM note
ORDER BY togglecase(oid)
This should result in:
1 "1"
2 "1,1"
3 "1,1,a"
4 "1,1,a,1"
5 "1,1,A"
6 "1,1,A,1"
The code is untested except for the togglecase function.

Answer 2

You are getting that result because the sorting is pecified to be NOCASE. That means that "a" and "A" are equals. So, first the rows with "a/A" and nothing after, and then rows with "a/A" and data after.
If you make the query CASE SENSITIVE, you will get a different result. BUT "A" comes befores "a" in case sensitive sort:
SELECT id, oid
FROM note
ORDER by oid
Results:
1 "1"
2 "1,1"
5 "1,1,A"
6 "1,1,A,1"
3 "1,1,a"
4 "1,1,a,1"