Thread: Column limits in table/ views
I have 560 columns of NUMERIC(10,14). To not run up against max column restraints, I split the information into two tables. Does the column limit on tables imply the same limit for views or selects or could I potentially select a row across both tables and make a view that hides the split?
On Fri, 2003-06-06 at 18:02, A.M. wrote: > I have 560 columns of NUMERIC(10,14). To not run up against max column > restraints, I split the information into two tables. Does the column > limit on tables imply the same limit for views or selects or could I > potentially select a row across both tables and make a view that hides > the split? The limit is documented as having to do with the size of a block. The largest a single row can become is 8k with primitive types (text, and other variable length types will 'overflow' into another area -- see TOAST). Selects should be able to return more columns than that. Both views and tables create a ROW TYPE to represent it, which is where the limitation is. Thus, I would not expect you to be able to create a view. -- Rod Taylor <rbt@rbt.ca> PGP Key: http://www.rbt.ca/rbtpub.asc
"A.M." <agentm@cmu.edu> wrote: > I have 560 columns of NUMERIC(10,14). To not run up against max column > restraints, I split the information into two tables. Does the column > limit on tables imply the same limit for views or selects or could I > potentially select a row across both tables and make a view that hides > the split? Hi, just for curiosity, can I known why do you need a table or a view with more then 560 Columns ? Usually have a big table like yours is sign of a not good design. Regards Gaetano Mendola
Rod Taylor <rbt@rbt.ca> writes:
> On Fri, 2003-06-06 at 18:02, A.M. wrote:
>> I have 560 columns of NUMERIC(10,14). To not run up against max column=20
>> restraints, I split the information into two tables. Does the column=20
>> limit on tables imply the same limit for views or selects or could I=20
>> potentially select a row across both tables and make a view that hides=20
>> the split?
> The limit is documented as having to do with the size of a block. The
> largest a single row can become is 8k with primitive types (text, and
> other variable length types will 'overflow' into another area -- see
> TOAST).
> Selects should be able to return more columns than that. Both views and
> tables create a ROW TYPE to represent it, which is where the limitation
> is. Thus, I would not expect you to be able to create a view.
But a view row is never stored on disk, so the block-size limit doesn't
come into play. You will still be constrained by the max column count
(1600), because that comes from the tuple header layout --- the size of
the header plus null bitmap has to fit into a uint8 field. But a view
with 560 columns would work.
I think some performance issues might come up if you actually try to
select all the columns at once, because there are places whose behavior
is O(N^2) in the number of columns. Dunno whether this effect will be
noticeable with ~560 columns though.
regards, tom lane