I haven't done the work yet to add a column to pg_aggregate, so this just knows about optimizing a couple of hard-wired cases (int4 and text). Other than that it's reasonably complete, I think. Comments?
Looks good :
regression=# explain select max(unique1) from tenk1;
QUERY PLAN
---------------------------------------------------------------------------------------------------------
Result (cost=0.15..0.16 rows=1 width=0)
InitPlan
-> Limit (cost=0.00..0.15 rows=1 width=4)
-> Index Scan Backward using tenk1_unique1 on tenk1 (cost=0.00..1512.59 rows=10000 width=4)
(4 rows)
The handling of nulls is a little unexpected (still todo?) :
regression=# insert into tenk2 (unique1,unique2) values(null, 10000); INSERT 0 1 regression=# select max(unique1) from tenk2; max -----
(1 row) regression=# set enable_indexscan=0; SET regression=# select max(unique1) from tenk2; max ------ 9999 (1 row)
cheers
Mark
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