Below are snippets from Diane Brown's messages (from former Mers list).

Ivan
http://www.volny.cz/iprenosil/interbase

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SQL92 includes the following note:
"Note: It is the intention that no <key word> specified in this
International Standard or revisions thereto shall end with an <underscore>."
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For what it's worth, there is a note in SQL99 that says:
"Assurance that a <regular identifier> will not become a <reserved word> in
a possible future revision of ISO/IEC 9075 can be obtained by including a
<digit> or an <underscore> in the <regular identifier>, and by taking care
to avoid identifiers beginning with CURRENT_, SESSION_, SYSTEM_, or
TIMEZONE_, or ending in _LENGTH."
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