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NCHAR to CHAR conversions can occur as part of a comparison of CHAR and NCHAR data, or when specifically requested. This type of conversion is considered lossy because there there are some NCHAR characters that can not be represented in the CHAR type. When these characters are present in the NCHAR data, a substitution character from the CHAR character set is used instead. For single-byte character sets, this is usually hex 1A.
Depending on the setting of the on_charset_conversion_failure option, when a character cannot be converted, one of the following can happen:
a substitute character is used, and no warning is issued
a substitute character is used, and a warning is issued
an error is returned
Therefore, it is important to consider this option when converting from NCHAR to CHAR. See on_charset_conversion_failure option [database].