DB2 10.5 for Linux, UNIX, and Windows

nchar_mapping - National character mapping configuration parameter

This parameter determines the data type mapping for national character string data types in Unicode databases.

Configuration type: Database
Parameter type: Configurable online
Default [range]: GRAPHIC_CU16 [CHAR_CU32, GRAPHIC_CU32, GRAPHIC_CU16, NOT APPLICABLE]

If you are not using a Unicode database, the value of nchar_mapping is NOT APPLICABLE because there is no support for specifying national character string data types in non-Unicode databases.

The national character string data type mapping is as follows:

Table 1. Mapping between national character strings and data types
Parameter Value	NCHAR	NVARCHAR	NCLOB
CHAR_CU32	CHAR in string units `CODEUNITS32`	VARCHAR in string units `CODEUNITS32`	CLOB in string units `CODEUNITS32`
GRAPHIC_CU32	GRAPHIC in string units `CODEUNITS32`	VARGRAPHIC in string units `CODEUNITS32`	DBCLOB in string units `CODEUNITS32`
GRAPHIC_CU16	GRAPHIC in string units `CODEUNITS16`	VARGRAPHIC in string units `CODEUNITS16`	DBCLOB in string units `CODEUNITS16`

Effects of changing the value of nchar_mapping

Materialized query tables (MQTs) might contain different results after altering the nchar_mapping value. To ensure that previously created MQTs contain only data that adheres to the new format, refresh these MQTs by using the REFRESH TABLE statement.
The results of a trigger might be affected by the changed format. Altering the nchar_mapping value has no effect on data that has already been written.
Constraints that allowed data to be inserted into a table might, if reevaluated, reject that same data. Similarly, constraints that did not allow data to be inserted into a table might, if reevaluated, accept that same data. Use the SET INTEGRITY statement to check for and correct data in a table that might no longer satisfy a constraint.
After changing the value of nchar_mapping, recompile all static SQL packages that depend on the value of a generated column whose results are effected by the change in the nchar_mapping value. To find out which static SQL packages are effected, you must compile, rebind all the packages using the db2rbind command.
The value of an index with expression-based keys whose calculation is dependent on nchar_mapping will be different after changing the value of nchar_mapping. Drop and recreate all potentially impacted expression-based indexes after changing the value of nchar_mapping. If you are not sure that a particular expression-based index is impacted, it is best to drop and recreate the index to avoid incorrect values in the index.