Rick,
Welcome to the list - we try not to byte, er, bite...
I am trying to do a select that will display events by category, but
will NOT display a category name if it is empty (has no events).
2 tables: categories and events
events contains a field called category_id that corresponds to the id of
a category in categories.
=a 'clean' structure, and you understand how to join the two tables - and your basic
query appears below.
I am doing a 'while' loop for the events inside a 'while' loop for the
categories. It displays the category, then all events for that category.
=ouch! This is thinking in 'procedural logic', eg C, PHP, programming languages; not
'relational logic/algebra'
suited to a SQL RDBMS - but we know what you mean...
=you will need to expand the query (below) to display information from the events
table - currently the last
clause of your spec (above) is not implemented (below).
I am trying to find a simple way to NOT display the category if there
are no events in that category.
=check out the manual's discussion of IS [NOT] NULL, alternatively read up about
different types of 'joins'.
However I wouldn't get into that complication until you deal with the central issue
below (get the db to respond
with a superset of your data, then work on refining that result down to the level of
precision/exclusion you
require!)
This seems logical, but does not produce any output:
SELECT category from categories WHERE categories.id =
events.category_id
=On the face of it, you should get some answers back, except that you need to name
both of the tables involved
in the FROM clause.
=Are you using native MySQL at the command line, or a management tool? (or are you
being more complicated, and
calling MySQL from a programming language) Keep things simple - use native SQL first
(no interfacing issues),
then cut-and-paste into a more complicated 'vehicle', if that's what you want to do.
=If a problem persists at this level, could you come back to us the two table
definitions and maybe some sample
data?
I can envision ways of getting this result that are more complicated
that they should be. Is there a fairly simple way ?
BTW, I just joined this list and this is my first post. Let me know if
I am being unclear.
=where there's a will, there's a way!
=dn
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