How to select sqlite order by char and number key? - objective-c

Question

Some value of col in sqlite database:
a1b2
a2b3
a1b10
a10b1
if use order by in sql it will be:
a10b1
a1b10
a1b2
a2b3
I want it like NSNumericSearch of objc like this:
a1b2
a1b10
a2b3
a10b1
How do I write the SQL statements?

Answer 1

Start by creating a custom collating function:
int compare_natural(void *data, int len1, const void *str1, int len2, const void *str2) {
if (str1 && len1 > 0 && str2 && len2 > 0) {
NSString *s1 = [[NSString alloc] initWithBytesNoCopy:(void *)str1 length:len1 encoding:NSUTF8StringEncoding freeWhenDone:NO];
NSString *s2 = [[NSString alloc] initWithBytesNoCopy:(void *)str2 length:len2 encoding:NSUTF8StringEncoding freeWhenDone:NO];
// The use of NSNumericSearch is required for your need.
// The others are options depending on your needs
NSComparisonResult res = [s1 compare:s2 options:NSCaseInsensitiveSearch | NSNumericSearch | NSDiacriticInsensitiveSearch];
return res;
} else if (str1 && len1 > 0 && (!str2 || len2 == 0)) {
return -1; // empty strings to the end of the list (optional)
} else if (str2 && len2 > 0 && (!str1 || len1 == 0)) {
return 1; // empty strings to the end of the list (optional)
} else {
return 0;
}
}
Then register the custom collator. This needs to be done after you open the database.
// dbRef is your sqlite3 database reference
int rc = sqlite3_create_collation(dbRef, "BYNUMBER", SQLITE_UTF8, NULL, &compare_natural);
Then update your query so it ends with "COLLATE BYNUMBER"
SELECT some_col ORDER BY some_col COLLATE BYNUMBER;