What does COLLATE LOCALIZED ASC stand for?

问题

private Cursor getContacts()
    {
        // Run query
        Uri uri = ContactsContract.Contacts.CONTENT_URI;
        String[] projection = new String[] {
                ContactsContract.Contacts._ID,
                ContactsContract.Contacts.DISPLAY_NAME
        };
        String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP + " = '" +
                (mShowInvisible ? "0" : "1") + "'";
        String[] selectionArgs = null;
        String sortOrder = ContactsContract.Contacts.DISPLAY_NAME + " COLLATE LOCALIZED ASC";

        return managedQuery(uri, projection, selection, selectionArgs, sortOrder);
    }

What does COLLATE LOCALIZED ASC stand for?

回答1:

Collate is just fancy speak for sort (well sort of). So this is sort ordering based on localized preferences (i.e. current language's alphabet and conventions) in ascending order.

回答2:

It instructs SQLite to sort non-ASCII characters appropriately. Chars with diacritics (some call them accents) have higher byte codes than the character Z, so a plain ASCII sort wouldn't fit to many foreign languages.

For example, the capital A char's byte code is 0x41 and the capital Z char's is 0x5A. Then we have the Á (capital A accute) which code in Unicode is 0x00C1. So a plain byte code sort would result the Á to be after the Z.

But in languages that have this kind of characters the convention is to put those with diacritics as if they didn't have the diacritic. So the Á should be together with the plain A, at least before B.

And to illustrate, we have below a list of names sorted using their bytecode:

Brenda
Debby
George
Álvaro
Érico

Now using the COLLATE LOCALIZED it would sort by the "base" of the character:

Álvaro
Brenda
Debby
Érico
George

回答3:

COLLATE is an SQL operator that lets you override the default sort order for strings. For example, "COLLATE NOCASE" does case-insensitive comparison, and "COLLATE BINARY" does a case-sensitive comparison.

The SQLite C interface lets you define custom collations (http://www.sqlite.org/c3ref/create_collation.html).

来源：https://stackoverflow.com/questions/2380706/what-does-collate-localized-asc-stand-for

标签

java

android

sqlite

contactscontract