Hi everyone,
Short version: is there a particularly good reason why the modulus operator
(%) isn't supported in Sequel VirtualRow, and neither are the equality
operators (==, !=)? I've produced a PoC patch to do the former, and would
have a crack at the latter, if they would be accepted. However, given how
simple it was to implement modulus, I can't help but think there is a very
good reason why they aren't in there.
Long version:
I tried to define a where clause which contained a modulus calculation, like
so:
db[:ex].where { col % 3 == 0 }
Much to my surprise, this bombed, telling me
NoMethodError: undefined method `%' for #<Sequel::SQL::Identifier
@value=>:col>
"Hmm, OK", says I, "I'll see if I'm doing this totally wrong, by trying
division":
db[:ex].where { col / 3 == 0 }
This doesn't exception out, but instead produces the SQL
SELECT * FROM "ex" WHERE false
That's... not right.
I've verified that the following *does*, in fact, work in PgSQL, at least:
SELECT * FROM ex WHERE col % 3 = 0
With a bit of digging around, I've discovered that, unlike the "basic"
arithmetic operators (+, -, *, /), modulus isn't part of the SQL standard.
However, neither is !=, and Sequel seems quite happy to use that in
preference to the standard version, <>, so my intuition is that Sequel isn't
*absolutely* strict about SQL standards-compliance. Every DB engine I've
looked into seems to support modulus, either via '%' or 'MOD' (or, if you're
MySQL, *both*). There even appears to be support for converting '%' to
'MOD' in the Access adapter, so it's very strange that Sequel is overlooking
it elsewhere. I keep coming back to the idea that there *must* be a good
reason for not supporting it, but I'm stumped for what that might be.
On the equality operator issue, I know that it's quite a bit trickier to
support != (since Ruby just calls #== and inverts the result), but even if
it weren't practical to support, it'd be nice if Sequel complained about its
use, rather than chucking out an absolute 'false' (or 'true', as happens if
you use != somewhere -- that could get nasty).
I'm happy to implement either of those two ideas -- either trying to get
==/!= to work in VirtualRow, or else throwing an exception when they're
used, so that at least people don't accidentally end up with unexpected
results. Just let me know which one would be better.
- Matt
--
"For once, Microsoft wasn't exaggerating when they named it the 'Jet Engine'
-- your data's the seagull."
-- Chris Adams
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