[PATCH] Erase the distinctClause if the result is unique by definition
I forgot to mention this in the last round of comments. Your patch was actually removing distictClause from the Query structure. Please avoid doing that. If you remove it, you are also removing the evidence that this Query had a DISTINCT clause in it.
Yes, I removed it because it is the easiest way to do it. what is the purpose of keeping the evidence?
Julien's example provides an explanation for this. The Query structure is serialised into a view definition. Removing distinctClause from there means that the view will never try to produce unique results.
Suppose after a DDL, the prepared statement need to be re-parsed/planned
if it is not executed or it will prevent the DDL to happen.
The query will be replanned. I am not sure about reparsed though.
-- session 2
postgres=# alter table t alter column b drop not null; ALTER TABLE
-- session 1:
postgres=# explain execute st(1); QUERY PLAN ------------------------------------------------------------- Unique (cost=1.03..1.04 rows=1 width=4) -> Sort (cost=1.03..1.04 rows=1 width=4) Sort Key: b -> Seq Scan on t (cost=0.00..1.02 rows=1 width=4) Filter: (c = $1) (5 rows)
Since this prepared statement is parameterised PostgreSQL is replanning it every time it gets executed. It's not using a stored prepared plan. Try without parameters. Also make sure that a prepared plan is used for execution and not a new plan.
