Duplicate rows in NLSCASE INSENSITIVE databases

In a database that was created with the NLSCASE INSENSITIVE option, columns and expressions of NCHAR or NVARCHAR data types make no distinction between upper case and lower case letters, so that strings of these data types that have the same sequence of characters, but with letter case variants, evaluate as duplicates.

Queries that include the ALL, DISTINCT, or UNIQUE keywords might return results different from what the same query returns from a case-sensitive database into which the same character string values had been loaded. For example, the NVARCHAR strings "aCe", "ACE", and "AcE" evaluate as identical in databases that have the NLSCASE INSENSITIVE property, but the same three strings are processed as distinct values in case-sensitive databases.

Strings of type CHAR, LVARCHAR, and VARCHAR, however, are processed identically in NLSCASE SENSITIVE and in NLSCASE INSENSITIVE databases by queries that use the ALL, DISTINCT, or UNIQUE keywords to include or exclude duplicate rows. For more information about databases with the NLSCASE INSENSITIVE property, see Specifying NLSCASE case sensitivity and NCHAR and NVARCHAR expressions in case-insensitive databases.