On 04-Apr-2008, at 1:17 PM, Nicolas Williams wrote:
> On Fri, Apr 04, 2008 at 01:06:58PM -0700, Steven Fisher wrote:
>>> It's not necessarily the same as strcasecmp(). You can have per-
>>> column collations.
>>
>> Column names, not column contents. :) I don't like to have my C code
>> rely on the order of columns from a query. You can avoid depending on
>> parameter ordering with sqlite3_bind_parameter_index, but there
>> doesn't seem to be an equivalent for result columns.
>
> Sure there is:
>
> const char *sqlite3_column_decltype(sqlite3_stmt*,int);
> int sqlite3_column_type(sqlite3_stmt*, int iCol);
This would be useful but, again, that's not at all what I want. I'm
looking for column NAMES, not contents.
Maybe it'd be better to explain this with psuedo code.
This is what I want to do:
sqlite3_prepare_v2( db, "SELECT ColumnA,ColumnB FROM ATable;", -1,
&stmt, &tail );
int column_a_idx = sqlite3_column_index( stmt, "ColumnA" );
int column_b_idx = sqlite3_column_index( stmt, "ColumnB" );
while ( sqlite3_step( db ) == SQLITE_ROW ) {
sqlite3_column_text( stmt, column_a_idx, avalue );
sqlite3_column_text( stmt, column_b_idx, bvalue );
}
sqlite3_fianlize( stmt );
I'm avoiding hard an expectation here that column a is in position 0,
and column b in position 1. This doesn't matter for such a simple
query, but for larger queries future proofing the code from changes to
queries is just good practice.
This code won't run, though, because sqlite3_column_index doesn't
exist. I need to write my own. That means I need to replace
sqlite3_column_index with find_column, which is defined something like
this:
int find_column( sqlite3_stmt * stmt, const char * name )
{
int count = sqlite3_column_count( stmt );
for ( int i = 0; i < count; i++ ) {
const char * column = sqlite3_column_name( stmt, i );
if ( stricmp( column, name ) == 0 )
return i;
}
return -1;
}
There's two problems here:
1. I need to define something to find the column at all. There's a way
to find binding indexes by name, so why not columns? I understand the
need to avoid code bloat, but surely a way to future proof code by not
having to hard-coding column positions is worth the size delta.
2. I need to use stricmp for comparing column names. I'd rather use
the same comparison that sqlite3 uses for comparing column NAMES.
The first problem could be fixed by adding sqlite3_column_index, the
second by adding sqlite3_stricmp. The first would (probably?) increase
the size of sqlite3 slightly, the second would only make an internal
function publicly available.
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