[Qgis-user] Layer extent

[Marco Casalboni]

Hi Alexandre,
and thanks for the feedback

I'm sorry but I don't understand the 2 solutions you advised.

Let's see if I can explain my case better.
I am using SqlServer and I set up a test project including that view and a
normal spatial table.
Looking at the initialization queries in SQLServer profiler, I noticed that
both entities run the same queries. But if the spatial_index_tessellations
lookup query returns no data, then QGIS tries to retrieve the extent with a
full table scan.

In order the queries are:
1) get the computed columns (almost useless for me)
SELECT name FROM sys.columns WHERE is_computed = 1 AND object_id = xxx

2) get columns metadata (in some cases useless for me)
exec sp_columns @table_name = xxx

3) get table pks (useless for me)
exec sp_pkeys @table_name = xxx

4) get extent from index
SELECT min(bounding_box_xmin), min(bounding_box_ymin),
max(bounding_box_xmax), max(bounding_box_ymax) FROM
sys.spatial_index_tessellations WHERE object_id = xxx

5) if 4 returns no data, then compute the extent from full scan (2 queries)
5-1) Compute a binary checksum (????? and why 42?)

select min([SHAPE].STPointN(1).STX), min([SHAPE].STPointN(1).STY),
max([SHAPE].STPointN(1).STX), max([SHAPE].STPointN(1).STY), count(*) from
xxx WHERE (ABS(CAST((BINARY_CHECKSUM([[OBJECTID]])) as int)) % 100) = 42

5-2) actually compute the extent from full scan
select min([SHAPE].STPointN(1).STX), min([SHAPE].STPointN(1).STY),
max([SHAPE].STPointN(1).STX), max([SHAPE].STPointN(1).STY), count(*) from
xxx
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