Re: [GENERAL] Why does increasing the precision of a numeric column rewrites the table?

Thomas Kellerer <spam_eater@gmx.net> writes:
> I don't understand why going from numeric(12,2) to numeric(15,3) would require a table rewrite.

The comment for numeric_transform explains this:
* Flatten calls to numeric's length coercion function that solely represent* increases in allowable precision.  Scale
changesmutate every datum, so* they are unoptimizable.  Some values, e.g. 1E-1001, can only fit into an* unconstrained
numeric,so a change from an unconstrained numeric to any* constrained numeric is also unoptimizable. 

The issue is basically that changing '1.00' to '1.000' requires a change
in the actually-stored value.
        regards, tom lane


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