Create a table with 1600 fields (reaching the upper limit), then drop several fields and create new ones, but the addition failed.
test=# alter table t1 add column co1599 int;
ALTER TABLE
test=# alter table t1 add column co1600 int;
ALTER TABLE
test=# alter table t1 add column co1601 int;
psql: ERROR: table can have at most 1600 columns
then, I drop column co1600 and add it again, failed:
test=# alter table t1 drop column co1600;
ALTER TABLE
test=# alter table t1 add column co1600 int;
psql: ERROR: table can have at most 1600 columns
then, I drop column co1600 again:
test=# alter table t1 drop column co1600;
psql: ERROR: column "co1600" of relation "t1" dose not exist
