{SQLFIND:[db.dbo.client.emailaddress],[email]} would return the primary key value for the table client for the FIRST match found in the table where a value is found in the emailaddress that equal [email].

{SQLINDEX:[db.dbo.client.emailaddress],[vRecordId,S]} would return the value in the column emailaddress where the primary key value = the session variable vRecordId.

Couldnt you accomplishing both of those with this syntax?

{SUBQUERY,Name="sqlfind",Query="Select top 1 EmailID from db.dbo.client where emailaddress='[email]'",Format="[EmailID]"}

{SUBQUERY,Name="sqlindex",Query="Select top 1 emailaddress from db.dbo.client where EmailID='[vRecordId,S]'",Format="[emailaddress]"}

Yeah, I guess....