Keith Medcalf Sent: Monday, December 18, 2017 1:07 PM
To: SQLite mailing list <sqlite-users@mailinglists.sqlite.org>
Subject: Re: [sqlite] Odd question
>>I investigated a further while exploring some of the list
>>suggestions. The app halts with an error unless
>>sqlite3_column_count() > 0. That means I misspoke when I mentioned
>>that the sql statement needed to return at least one row. I’m not
>>sure if that makes a difference, though.
> That makes a *huge* difference. sqlite3_column_count() is available after
> the prepare and before the first step.
Yes, the sqlite3_column_count() call happens after prepare() and before step().
>This means that the statement can be cancelled BEFORE it is executed
>(step'ed). "returns no rows" can only be determined by running (step'ing) the
>statement and requires the statement to be both prepared and run (and that it
>returns SQLITE_DONE with no SQLITE_ROW).
Right, all of the statements are step'd regardless of the result of
sqlite3_column_count(). SQLITE_DONE is returned from the first step() for
insert queries.
>In the former case all statements which are not select/pragma statements
>returning data do not have to be run.
All the statements are run, the check for column count happens further
downstream
>In the latter case, all statements will be run and you will get the "no data
>was returned" if no data was returned.
Yes, all statements are run but the error comes from the fact that
sqlite3_column_count() == 0
In pseudocode, it's
prepare("insert...") //okay
int num_col = sqlite3_column_count() //okay
step() until sqlite_done //okay
assert(num_col > 0) // blows up here, even though the query was successful
So effectively I need sqlite3_column_count() > 0 in order to bypass the faulty
assertion.
Thanks for your help in pushing me to think about it and describe it more
clearly- even if we don't find a solution it's a helpful conversation.
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