>> Var Alice := Db.SelectRecord('SELECT * FROM client WHERE client_name = ?', [
>> 'alice' ]);
>>
>> 1. If I drop record for "alice" from db and then access column data in
>> prepared stmt will it work OK?
>
> If the select statement wasn't reset or finalized, you won't be able to
> delete a record from the database (or, in WAL journaling mode, you would be
> able to, but the reader would still see original data).
Well, if he uses the same connection used to prepare the statement,
then he will be able to delete record even in normal journaling mode.
What happens in this case is undefined. It might be that column data
will be still accessbile, it might be you get some garbage, it might
be an access violation.
>> 2. Can I drop client table while having such prepared stmt not closed?
I think table client cannot be dropped altogether until all statements
using it are reset/finalized.
Pavel
On Fri, Oct 19, 2012 at 12:49 PM, Igor Tandetnik <itandet...@mvps.org> wrote:
> Григорий Григоренко <grigore...@mail.ru> wrote:
>> I am using prepared stmts to cache selected record for later use. I have a
>> wrapper class, that has methods like AsString(name),
>> AsFloat(name) etc to extract data for a column name.
>>
>> I prepare, bind and then do Sqlite3_step() to get record. Later I use
>> sqlite3_column_XXX() to access data.
>>
>> My concern is - do open selective prepared stmts depend on something in db
>> or lock something in db?
>
> Yes, until you call sqlite3_reset or sqlite3_finalize. For as long as the
> statement is "active" (meaning, sqlite3_reset or sqlite3_finalize has not
> been called after the most recent sqlite3_step call), it holds a read
> transaction open.
>
>> Var Alice := Db.SelectRecord('SELECT * FROM client WHERE client_name = ?', [
>> 'alice' ]);
>>
>> 1. If I drop record for "alice" from db and then access column data in
>> prepared stmt will it work OK?
>
> If the select statement wasn't reset or finalized, you won't be able to
> delete a record from the database (or, in WAL journaling mode, you would be
> able to, but the reader would still see original data).
>
>> 2. Can I drop client table while having such prepared stmt not closed?
>
> What do you mean by "closed" here?
>
>> 3. If I have a lot of such stmts (100 or more) will it somehow affect
>> performance of SQLite or waste lots of memory?
>
> No, not really. There is a reasonably small data structure associated with a
> prepared statement, on the order of a few hundred bytes perhaps.
>
>> Are there some kind of cursors for each selecting prepared stmt?
>
> In a sense. After a call to sqlite3_step and before a call of sqlite3_reset
> or sqlite3_finalize, you might think of a statement handle as a form of a
> cursor. Each subsequent sqlite3_step call advances this cursor forward by one
> row.
>
>> 4. If there is a cursor, maybe there is a way to disconnect a cursor from
>> stmt keeping the single record still available?
>
> No, short of making a copy of every column's value.
> --
> Igor Tandetnik
>
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