DB2 SQL Mixed data in character strings

Mixed character data and graphic data are always allowed for Unicode, but for EBCDIC and ASCII, the specific installation of DB2® determines whether mixed data can be used.

The field MIXED DATA on installation panel DSNTIPF can have the value YES or NO for ASCII or EBCDIC character strings. The value YES indicates that character strings can contain a mixture of SBCS and DBCS characters. The value NO indicates that they cannot. Mixed character data and graphic data are always allowed for Unicode; that is the MIXED DATA field does not have an effect on Unicode data.

For static SQL statements, the value of the CCSID SQL processing option or the derived CCSID for the DB2 coprocessor determines whether ASCII or EBCDIC character strings can contain mixed data. If a mixed CCSID is used, mixed strings are allowed. If a single-byte CCSID is used, mixed strings are not allowed.

For dynamic SQL statements, the CCSID that is selected to convert the dynamic statement text to UTF-8 determines whether ASCII or EBCDIC character strings can contain mixed data. The CCSID for a dynamic statement is determined from the SQLDA override (if any) for the host variable on the PREPARE statement, the value of the CURRENT ENCODING SCHEME special register, and the ENCODING bind option.

The value of MIXED DATA affects the parsing of SQL character string constants, the execution of the LIKE predicate, and the assignment of character strings to host variables when truncation is needed. It can also affect concatenation, as explained in Expressions with the concatenation operator. A value that applies to a statement executed at the local DB2 also applies to any statement executed at another server. An exception is the LIKE predicate, for which the applicable value of MIXED DATA is always the one at the statement's server.

The value of MIXED DATA also affects the choice of system CCSIDs for the local DB2 and the choice of data subtypes for character columns. When this value is YES, multiple CCSIDs are available for ASCII and EBCDIC data (SBCS, DBCS, and MIXED). The CCSID specified in the ASCII CCSID or EBCDIC CCSID field is the MIXED CCSID. In this case, DB2 derives the SBCS and MIXED CCSIDs from the DBCS CCSID specified installation panel DSNTIPF. Moreover, a character column can have any one of the allowable data subtypes—BIT, SBCS, or MIXED.

On the other hand, when MIXED DATA is NO, the only ASCII or EBCDIC system CCSIDs are those for SBCS data. Therefore, only BIT and SBCS can be data subtypes for character columns.