On 30 Jun 2011, at 10:28, Igor Tandetnik wrote:
> On 6/30/2011 1:15 PM, Simon Gornall wrote:
>> Is it possible to get the columns operated on by a WHERE clause from the
>> sqlite3_stmt once it's been prepared ?
>>
>> I looked at the sqlite3_set_authorizer, but it doesn't seem to have
>> an action code for examining WHERE - the only codes that use
>> column/table info are UPDATE (which I already know) and READ (I don't
>> know what this is used for but it sounds more general than I'd
>> need).
>
> READ action gives you the columns that the statement needs to read, for
> any reason. They may be mentioned in SELECT, WHERE, ORDER BY, LIMIT, ON
> and other clauses - whenever an expression is allowed by the syntax.
>
> Seems to be just what you need.
Well, perhaps I'm missing something, but if the statement for which I'm caching
results was something like
SELECT * FROM tableName WHERE columnName = zzz;
I'd only want to clear the results cache when statements like:
UPDATE tableName set columnName = xxx where id=yyy;
were processed. I'd specifically *not* want to clear the results-cache for the
above statement when I got:
UPDATE tableName set otherColumnName = xxx where id = yyy;
...because changing values in the column 'otherColumnName' can't affect the
results-list for a query only dependent on the column 'columnName'.
And I think the READ action would give me all the columns (because * was
selected) when processing the SELECT statement. In order to cross-match the
columns-for-the-select-statement and the columns-for-the-update, I need to know
only the columns in the criteria part of the SELECT statement, not those used
by any clause in the SELECT.
On 30 Jun 2011, at 10:23, Richard Hipp wrote:
>
> Would the update_hook be helpful here?
>
> http://www.sqlite.org/c3ref/update_hook.html
Well, I actually know the columns being updated at the update-stage already.
What I don't know is the set of columns that correspond to the criteria part of
the query statement for which I'm caching results. The update-hook doesn't
really help anyway (for this, I'm planning on using it for other stuff later
[grin]) because it only provides the {database|table|row-id} information, not
the columns-within-the-update statement.
Cheers
Simon
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