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2026-03-12 20:23:15

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tpt/demos/join_elimination.sql Normal file
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-- Oracle join elimiation demo by Tanel Poder (https://tanelpoder.com)
DROP TABLE o;
DROP TABLE u;
CREATE TABLE u AS SELECT * FROM all_users;
CREATE TABLE o AS SELECT * FROM all_objects WHERE owner IN (SELECT username FROM all_users);
ALTER SESSION SET statistics_level = ALL;
-- set echo on
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner AND u.created IS NULL;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
ALTER TABLE u ADD PRIMARY KEY (username);
ALTER TABLE o ADD CONSTRAINT fk_u FOREIGN KEY (owner) REFERENCES u(username);
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
ALTER TABLE o DISABLE CONSTRAINT fk_u;
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
ALTER TABLE o ENABLE NOVALIDATE CONSTRAINT fk_u;
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
ALTER TABLE o ENABLE VALIDATE CONSTRAINT fk_u;
SELECT COUNT(*) FROM u, o WHERE u.username = o.owner;
SELECT * FROM TABLE(dbms_xplan.display_cursor(format=>'+OUTLINE -NOTE'));
-- set echo off