Ref: http://developer.postgresql.org/pgdocs/postgres/errcodes-appendix.html
It seems to me that the second and the third column in that table are
redundant. The third is just the second with underscores and lower-case
letters. I find this pretty confusing, first because of the sheer
(apparent) volume of information, and second because one might be led to
believe that there is a difference between the columns hidden somewhere.
I suppose at one point it was the intent that the second column contain
a human-readable explanation, but that hasn't been realized.
Also, the sentence above the table "The PL/pgSQL condition name for each
error code is the same as the phrase shown in the table, with
underscores substituted for spaces. For example, code 22012, DIVISION BY
ZERO, has condition name DIVISION_BY_ZERO." is redundant or obsolete.
I think we should just remove the second column from the table and
rephrase the paragraph above it accordingly. At some point in the
future we could introduce a separate optional data field that adds
actual additional information about the error codes.