36 lines
963 B
MySQL
36 lines
963 B
MySQL
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-- Copyright 2018 Tanel Poder. All rights reserved. More info at http://tanelpoder.com
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-- Licensed under the Apache License, Version 2.0. See LICENSE.txt for terms & conditions.
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-- view merging
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select * from dual;
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select * from table(dbms_xplan.display_cursor);
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create or replace view v as select * from dual;
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select * from (select * from v);
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alter session set "_simple_view_merging"=false;
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select * from (select * from v);
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alter session set "_simple_view_merging"=true;
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select * from (select /*+ NO_MERGE */ * from v);
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select * from (select rownum r, v.* from v);
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-- scalar subqueries, run a subquery for populating a value in a single column or a row (9i+)
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select owner, count(*) from test_objects o group by owner;
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-- another way (excludes nulls if any)
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select u.username, (select count(*) from test_objects o where u.username = o.owner) obj_count from test_users u;
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select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
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