Patrick Welche <prlw1@newn.cam.ac.uk> writes:
> What is the difference between the following?
> transatlantic=# select count(*) from trans;
This is a SQL-spec-mandated special case meaning "count the number of rows".
> transatlantic=# select count(trans.flowindex) from trans;
This counts the number of non-null values of trans.flowindex. Also
per spec.
> transatlantic=# select count(trans.*) from trans;
ERROR: Memory exhausted in AllocSetAlloc(204)
This syntax is not legal per SQL spec. Postgres interprets it as a
command to count the number of non-null values of "trans.*", which in
this context is taken as being a whole-row variable. Unfortunately the
present implementation of whole-row variables leaks memory ...
I don't believe that a whole-row variable will ever be null, so the
end result is the same as count(*). You may as well spell it in the
spec-approved fashion.
regards, tom lane
