Re: Conjunction junction

"Alan" <alan_at_erols.com> wrote in message news:2unbuhF2cbaliU1_at_uni-berlin.de...
> UNION. Of course this can be done procedureally, but the XOR I described
> would have allowed it in straight SQL. Maybe call it an IOR (Immediate OR)
> if XOR is confusing.

There are 2 separate concepts:
1. what connectors between the boolean expressions are allowed, and 2. row limit "predicate".

Admittedly item #2 would be different in different SQL dialects. For example

SELECT stock_location
FROM pennants
WHERE (color = 'red' OR color = 'green')

and rownum <=1
^^^^^^^^^^^^

Alternatively, it might be the client that controls how many rows are fetched.

Performance of the above query is completely different topic. For example, optimizer might decide to convert this query into a concatenation. It executes the first branch, and the row satisfies the condition color = 'red', then it goes to the output, and execution stops immediately. Otherwise, it would follow to the second branch. Alternative execution plan is what you suggested: it iterates the relation tuples and checks the [complex] condition color = 'red' OR color = 'green' and stops as soon as a tuple is found. Received on Mon Nov 01 2004 - 12:41:20 CST