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Collations and Linguistic Sorting


As stated in the previous section, character and national character data is sorted according to specific collations.

A collation, also known as a collating sequence, is a database object containing a set of rules that determines how character strings are compared, searched and alphabetically sorted. The rules in the collation determine whether one character string is less than, equal to or greater than another. A collation also determines how case-sensitivity and accents are handled.

You can specify a different collation for ordering characters when you create or alter a table or create a domain.

If you have specified a collation for a column, the collation is used implicitly in SQL statements.

You only need to explicitly use a collate clause in SQL statements if you want to override the default collation or the collation you specified when creating or altering the column or creating the domain.

For more information, see Collations.

Since Unicode is a universal character set the Unicode sorting order can be employed on any arbitrary character set that is a subset of Unicode.

The default Unicode sorting order is provided in http://www.unicode.org/reports/tr10/allkeys.txt (Unicode 3.1.1 mapping). This table (the Default Unicode Collation Element Table) provides a mapping from characters to collation elements for all the explicitly weighted characters.


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