On 05/20/2017 06:17 PM, graf0 post.pl wrote:
Hello,
I'm trying to implement vtable, and I don't understand what is meaning of usable
field in sqlite3_index_constraint struct?
Can I assume it will be false when my vtable is joined by that field with some
other table?
Basically just that. Say "vtab" is your virtual table and "tbl" a normal
table. If you do:
SELECT * FROM vtab, tbl WHERE vtab.a=? AND vtab.b=tbl.c
then the sqlite3_index_info structure will contain two constraints. The
xBestIndex method will be invoked twice, once with only vtab.a=? marked
as enabled and once with both of the constraints enabled. So that the
planner knows the cost of using virtual table vtab as both the inner and
outer loop of the join.
Dan.
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