2026-03-12 20:23:15

tpt/demos/countstar.sql

@@ -0,0 +1,52 @@
+-- Copyright 2018 Tanel Poder. All rights reserved. More info at http://tanelpoder.com
+-- Licensed under the Apache License, Version 2.0. See LICENSE.txt for terms & conditions.
+
+-- count(columnX) is slower than count(*) or count(1)
+
+drop table t;
+create table t cache as select * from v$session;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert into t select * from t;
+insert /*+ append */ into t select * from t;
+commit;
+insert /*+ append */ into t select * from t;
+commit;
+insert /*+ append */ into t select * from t;
+commit;
+insert /*+ append */ into t select * from t;
+commit;
+insert /*+ append */ into t select * from t;
+commit;
+insert /*+ append */ into t select * from t;
+commit;
+
+exec dbms_stats.gather_table_stats(user, 'T');
+
+-- to get better rowsource level timing accuracy
+alter session set "_rowsource_statistics_sampfreq"=1;
+
+select /*+ gather_plan_statistics */ count(*) from t;
+
+set timing on
+
+select /*+ gather_plan_statistics */ count(*) from t;
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
+
+select /*+ gather_plan_statistics */ count(1) from t;
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
+
+select /*+ gather_plan_statistics */ count(sid) from t;
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
+
+select /*+ gather_plan_statistics */ count(state) from t;
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
+
+-- set back to default
+alter session set "_rowsource_statistics_sampfreq"=128;