Hello!
Over at python.org there is a bug report that its sqlite3 module sometimes
doesn't correctly deserialize a typed column. From my limited understanding
it boils down to the following once you go down to sqlite's C API:
#include <stdio.h>
#include "sqlite3.h"
int main(int argc, char **argv)
{
sqlite3 * db;
sqlite3_stmt * statement;
const char * type;
printf("%s\n", sqlite3_libversion());
sqlite3_open(":memory:", &db);
sqlite3_exec(db, "create table demo (alpha custom);", 0, 0, 0);
sqlite3_prepare_v2(db, "select * from (select alpha from demo union all
select alpha from demo) order by alpha", -1, &statement, NULL);
type = sqlite3_column_decltype(statement, 0);
printf("decltype: %s\n", type);
sqlite3_prepare_v2(db, "select * from (select alpha from demo union all
select alpha from demo)", -1, &statement, NULL);
type = sqlite3_column_decltype(statement, 0);
printf("decltype: %s\n", type);
return 0;
}
Long time no write C, I hope it doesn't show ;)
$ gcc demo.c sqlite3.c -lpthread -ldl
$ ./a.out
3.8.3.1
decltype: (null)
decltype: custom
A minor change (the order by clause) defeats type detection.
Even taking http://sqlite.org/c3ref/column_decltype.html
"""
If this statement is a SELECT statement and the Nth column of the returned
result set of that SELECT is a table column (not an expression or subquery)
then the declared type of the table column is returned. If the Nth column of
the result set is an expression or subquery, then a NULL pointer is
returned.
"""
into account I would have expected either NULL or "custom" for both queries.
PS: the original bug report is http://bugs.python.org/issue20587
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