>>> Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Alvaro Herrera <alvherre@xxxxxxxxxxxxxxxxx> writes: >> Ow Mun Heng wrote: >>> If it were this simple a change, I'm not certain why (I believe) PG is >>> checking each and every row to see if it will fit into the new column >>> definition/type. > >> Because the code that does the ALTER TYPE is very generic, and it >> doesn't (yet) have an optimization that tells it to skip the check and >> the possible table rewrite in the cases where it's obviously not needed >> (like this one). > > Awhile back I looked into teaching ALTER TYPE that it needn't rewrite > if the type conversion expression parses out as just a Var with > RelabelType, but it seemed that that wouldn't cover very much of the > use-cases where a human thinks that it's "obvious" that no rewrite > is needed. We wouldn't have to cover all possible cases for it to be useful. If there's some low-hanging fruit here, +1 for getting that. The cases which would most often save staff here some time are switching a varchar to a longer maximum length or switching between a domain which is varchar to plain varchar (or vice versa). -Kevin
