ICU, or International Components for Unicode, is an open source library developed and maintained by IBM. ICU facilitates software internationalization by providing Unicode support. SAP Sybase IQ implements certain character set conversions and collation operations using ICU.
Ideally, ICU should always be available for use by the database server. The following table specifies when and why ICU is needed:
| ICU is needed when... | Notes |
|---|---|
| Unicode Collation Algorithm (UCA) is used as the collation for the NCHAR or CHAR character set. | UCA requires ICU. |
| The database character set is not UTF-8, but is a multi-byte character set. | For password conversion from the database character set to UTF-8 (database passwords are stored in UTF-8, internally). |
| The client and database character sets are different, and when either of them is multi-byte (including UTF-8). This includes Unicode ODBC, OLE DB, ADO.NET, and SAP Sybase IQ JDBC applications, regardless of the database character set where at least one of these clients does not have ICU. | Proper conversion to and from a multi-byte character set requires ICU. |
| The database character set is not UTF-8 and conversion between CHAR and NCHAR values is required. | The database server requires ICU to convert UTF-8 to another character set. |
| An embedded SQL client uses an NCHAR character set other than UTF-8. | The database server requires ICU to convert UTF-8 to another character set. The default embedded SQL client NCHAR character set is the same as the initial client CHAR character set. This can be changed using the db_change_nchar_charset function. |
| The CSCONVERT or SORTKEY functions are used. The CSCONVERT function is called to convert between character sets that conform to the requirements of the third point above. | Character set conversion o and from a multi-byte character set requires ICU. Sortkey generation for many sortkey labels requires UCA, which, in turn, requires ICU. |
You can get correct character set conversion without ICU when both the database character set and client character set are single-byte and sqlany.cvf is available (all platforms), or if the operating system supports the conversion (Windows only). This is because single-byte to single-byte conversions can be processed without ICU if the sqlany.cvf file is available, or the host operating system has the appropriate converters installed.
For Unicode client applications, you are likely to get better combined client and database server performance when all clients have ICU installed, regardless of the database character set. This is because some of the required conversion activity may be offloaded from the database server to the client, and because fewer conversions are required.
Also, if you are using ODBC on Windows platforms, you must have ICU installed on the client, even for ANSI applications. This is because the driver manager converts ANSI ODBC calls to Unicode ODBC calls.