Am 12.07.22 um 20:13 schrieb Pierson Patricia L (Contractor):
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Do a count on the primary key. Will force index access and you don’t access the entire row which may be very long.
LIKE : select count(ID) from my_table;
If you do a COUNT(*) the database won't do anything different. That's a myth.
Just compare the execution plans.
db=# explain select count(anr) from auftrag;
QUERY PLAN
------------------------------------------------------------------------------------------
Finalize Aggregate (cost=11614.55..11614.56 rows=1 width=8)
-> Gather (cost=11614.33..11614.54 rows=2 width=8)
Workers Planned: 2
-> Partial Aggregate (cost=10614.33..10614.34 rows=1 width=8)
-> Parallel Seq Scan on auftrag (cost=0.00..9572.67 rows=416667 width=8)
(5 Zeilen)
db=# explain select count(*) from auftrag;
QUERY PLAN
------------------------------------------------------------------------------------------
Finalize Aggregate (cost=11614.55..11614.56 rows=1 width=8)
-> Gather (cost=11614.33..11614.54 rows=2 width=8)
Workers Planned: 2
-> Partial Aggregate (cost=10614.33..10614.34 rows=1 width=8)
-> Parallel Seq Scan on auftrag (cost=0.00..9572.67 rows=416667 width=0)
(5 Zeilen)
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