A sort sequence defines how characters in a character set relate to each other when they are compared and ordered. Different sort sequences are useful for those who want their data ordered for a specific language. For example, lists can be ordered as they are normally seen for a specific language. A sort sequence can also be used to treat certain characters as equivalent, for instance, a and A. A sort sequence works on all comparisons that involve:
SBCS sort sequence support is implemented using a 256-byte table. Each byte in the table corresponds to a code point or character in a SBCS code page. Because the sort sequence is applicable to character data, a CCSID must be associated with the table. The bytes in the sort sequence table are set based on how each code point is to compare to other code points in that code page. For example, if the characters a and A are to be treated as equivalents for comparisons, the bytes in the sort sequence table for their code points contain the same value, or weight.
UCS-2 sort sequence support is implemented using a multi-byte table. A pair of bytes within the table corresponds to a character in the UCS-2 code page. Only a subset of the thousands of characters in UCS-2 are typically represented in the table. Only those characters that are to compare differently (and possibly other characters in the same ward) will be represented in the table. The bytes in the sort sequence table are set based on how each character is to compare with other characters in UCS-2.
When two or more bytes (or pair of bytes for UCS-2) in a sort sequence table have the same value, the sort sequence is a shared-weight sort sequence. If every byte (or pair of bytes for UCS-2) in a sort sequence table has a unique value, the sort sequence is a unique-weight sort sequence. For many languages, unique- and shared-weight sort sequences are shipped on the AS/400 system as part of the operating system. If you need sort sequences for other languages or needs, you define them using the Create Table (CRTTBL) command.
It is important to remember that the data itself is not altered by the sort sequence. A weighted representation of the data is used for the comparison. In SQL, a sort sequence is specified on the CRTSQLxxx, STRSQL, and RUNSQLSTM commands. The SET OPTION statement can be used to specify the sort sequence within the source of a program containing embedded SQL. The sort sequence applies to all character comparisons performed in the SQL statements. The default sort sequence on the AS/400 system is the internal sequence that occurs when the hexadecimal representation of characters are used. This is the sequence you get when the SRTSEQ(*HEX) is specified. For programs precompiled with a release of the product that is earlier than Version 2 Release 3, the sort sequence is *HEX.
For more information on CCSIDs, see the book International Application Development, SC41-5603-01. For more information on sort sequences and the sequences shipped with the system, see the book National Language Support, SC41-5101-01.