Comment by pgjones
The presence of Absent removes the entire expression, and if that removal results in an empty clause (or group) it will remove that as well. For example if `a = Absent` `WHERE a = {a}` will remove everything, whereas `WHERE a = {a} AND b = {b}` will result in `WHERE b = {b}`.
> Do you support templating a sql tstring into an sql tstring for composition?
Yep
How do you know what the expression is though? Don’t you need to be parsing the SQL? If I have non standard SQL somewhere upstream in the text how does the parser cope?