double/real truncation incorrect

[fgwang7w]

Truncation of a decimal number leaves the precision as it was.

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Proposed Solution:
Fix in MathFunctions truncate(num,d) to drop double's precision digits after decimal point based on the value of d

[shixuan-fan]

I'm not particularly sure if SQL spec has definition about how truncate is supposed to work. If it is up to the engine implementation, then it sounds fine.

[fgwang7w]

Thanks for the feedback. looks like oracle and other ansi-sql db vendors only keeps the number of digits of the decimal point per specified input d.
https://docs.oracle.com/cd/B28359_01/server.111/b28286/functions208.htm#SQLRF06150
The implementation should be as straight-forward as to add support in scalar function for truncate double by dropping digits after decimal point.

[rongrong]

If most other databases remove trailing 0 we can change the behavior. Not sure what's the migration implications. @kaikalur thoughts?

[kaikalur]

Spec doesn't say anything about this. Looks like it's totally implementation dependent.