On Thu, Oct 01, 2009 at 11:37:40AM +0100, Thom Brown wrote: > I've read the PostgreSQL documentation page on the boolean datatype ( > http://www.postgresql.org/docs/8.4/static/datatype-boolean.html) to find out > what PostgreSQL's definition of a boolean is, as I believe it is distinctive > from a bit(1) datatype Yup, they're really for different things. AND, OR and NOT are defined for the BOOLEAN datatype and not for bit strings. > (as you can't max() a boolean.. not sure what an > efficient alternative to that is). bool_or and bool_and are aggregates that work over boolean data types. > However, I see that a boolean takes up 1 > byte of storage, which is 8 bits. Is this due to the fact that the value > can be null? I believe it's more to do with the fact that if you add a boolean column and then subsequently an int column then you're going to struggle to "pack" them efficiently. PG always puts columns on the "end" so that you can add a column in constant time (i.e. no need to rewrite the table in some common situations). Once you start doing this then packing is awkward and a single byte becomes much easier. Whether the value is NULL is stored elsewhere in the row. Yes, this could be made more efficient; whether it's worth it is a difficult question! > And does its storage as a byte affect indexing or query planning? Not sure which aspects you're referring to here, sorry. -- Sam http://samason.me.uk/ -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
