2026-03-12 20:23:15

tpt/demos/precompute_subquery.sql

@@ -0,0 +1,36 @@
+-- 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.
+
+drop table t1;
+drop table t2;
+
+set echo on
+
+create table t1 as select rownum a from dual connect by level < 10;
+create table t2 as select rownum+10 b from dual connect by level < 10;
+
+exec dbms_stats.gather_table_stats(user,'T1');
+exec dbms_stats.gather_table_stats(user,'T2');
+
+--alter session set events '10053 trace name context forever';
+--alter session set "_optimizer_trace"=all;
+--alter session set events '10046 trace name context forever, level 4';
+
+select * from t1;
+
+select * from t2;
+
+
+select a 
+from   t1
+where  a in (select b from t2);
+
+@x
+
+select a 
+from   t1
+where  a in (select /*+ PRECOMPUTE_SUBQUERY */b from t2);
+
+@x
+
+set echo off