2026-03-12 20:23:15

tpt/ast/01_sql_plan_layout_intro.sql

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+-- 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.
+
+-- view merging
+
+select * from dual;
+
+select * from table(dbms_xplan.display_cursor);
+
+create or replace view v as select * from dual;
+
+select * from (select * from v);
+
+alter session set "_simple_view_merging"=false;
+
+select * from (select * from v);
+
+alter session set "_simple_view_merging"=true;
+
+select * from (select /*+ NO_MERGE */ * from v);
+
+select * from (select rownum r, v.* from v);
+
+
+-- scalar subqueries, run a subquery for populating a value in a single column or a row (9i+)
+
+select owner, count(*) from test_objects o group by owner;
+
+-- another way (excludes nulls if any)
+
+select u.username, (select count(*) from test_objects o where u.username = o.owner) obj_count from test_users u;
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
+
+