unichar Datatype

The unichar and univarchar datatypes support the UTF-16 encoding of Unicode in SAP ASE. These datatypes are independent of the char and varchar datatypes, but mirror their behavior.

For example, the built-in functions that operate on char and varchar also operate on unichar and univarchar. However, unichar and univarchar store only UTF-16 characters and have no connection to the default character set ID or the default sort order ID, as char and varchar do.

Each unichar/univarchar character requires two bytes of storage. The declaration of a unichar/univarchar column is the number of 16-bit Unicode values. The following example creates a table with one unichar column for 10 Unicode values, requiring 20 bytes of storage:

create table unitbl (unicol unichar(10))

The length of a unichar/univarchar column is limited by the size of a data page, as is the length of char/varchar columns.

Unicode surrogate pairs use the storage of two 16-bit Unicode values (in other words, four bytes). Be aware of this when declaring columns intended to store Unicode surrogate pairs (a pair of 16 bit values that represent a character in the range [0x010000..0x10FFFF]). By default, SAP ASE correctly handles surrogates, and does not split the pair. Truncation of Unicode data is handled in a manner similar to that of char and varchar data.

You can use unichar expressions anywhere char expressions are used, including comparison operators, joins, subqueries, and so forth. However, mixed-mode expressions of both unichar and char are performed as unichar. The number of Unicode values that can participate in such operations is limited to the maximum size of a unichar string.

The normalization process modifies Unicode data so there is only a single representation in the database for a given sequence of abstract character (see Introduction to the Basics, in the Performance and Tuning Series: Basics for a discussion of normalization). Often, characters followed by combined diacritics are replaced by pre-combined forms. This allows significant performance optimizations. By default, the server assumes all Unicode data should be normalized.

• Relational Expressions
  All relational expressions involving at least one expression of unichar or univarchar, are based on the default Unicode sort order. If one expression is unichar and the other is varchar (nvarchar, char, or nchar), the latter is implicitly converted to unichar.
• Join Operators
  Join operators appear in the same manner as comparison operators. You can use any comparison operator in a join.
• Union Operators
  The union operator operates with unichar data much like it does with varchar data. Corresponding columns from individual queries must be implicitly convertible to unichar, or explicit conversion must be used.
• Clauses and Modifiers
  When unichar and univarchar columns are used in group by and order by clauses, equality is judged according to the default Unicode sort order. This is also true when using the distinct modifier.