Refinements to the optimizer overview and integration into the website. (CVS 2649)
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C Update\sthe\sFAQ\sto\sinclude\san\sentry\sabout\sbinary\sversus\sdecimal\snumbers.\s(CVS\s2648)
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D 2005-08-31T02:46:21
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C Refinements\sto\sthe\soptimizer\soverview\sand\sintegration\sinto\sthe\swebsite.\s(CVS\s2649)
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D 2005-08-31T03:13:12
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F Makefile.in 12784cdce5ffc8dfb707300c34e4f1eb3b8a14f1
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F Makefile.linux-gcc 06be33b2a9ad4f005a5f42b22c4a19dab3cbb5c7
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F README 9c4e2d6706bdcc3efdd773ce752a8cdab4f90028
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@ -276,7 +276,7 @@ F www/datatype3.tcl 1d14f70ab73075556b95e76a5c13e5b03f7f6c47
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F www/datatypes.tcl 7c786d2e8ff434346764534ec015966d17efce60
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F www/different.tcl d01064946c588db0a0e87563a30aef1b3efb4434
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F www/direct1b.gif 32b48b764244817b6b591898dc52a04299a7b8a7
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F www/docs.tcl 6c0b2c567404b15bd46a0cda2dc69615a8e679a8
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F www/docs.tcl 8fec3341bb9b0d0b09a0d4e33055825cdd69642c
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F www/download.tcl ceaa742d5b8137bce31e9dcc4e44494b38211490
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F www/dynload.tcl 02eb8273aa78cfa9070dd4501dca937fb22b466c
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F www/faq.tcl cdeb014235ac8030da593bde14a53240d4daa613
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@ -295,7 +295,7 @@ F www/omitted.tcl f1e57977299c3ed54fbae55e4b5ea6a64de39e19
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F www/opcode.tcl 5bd68059416b223515a680d410a9f7cb6736485f
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F www/optimizer.tcl d6812a10269bd0d7c488987aac0ad5036cace9dc
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F www/optimizing.tcl f0b2538988d1bbad16cbfe63ec6e8f48c9eb04e5
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F www/optoverview.tcl e16344994a91318965d573ecc9ef2848153d5bf0
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F www/optoverview.tcl b282361a505bddf85c43217095a66f47dbf6c788
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F www/pragma.tcl 44f7b665ca598ad24724f35991653638a36a6e3f
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F www/quickstart.tcl 6f6f694b6139be2d967b1492eb9a6bdf7058aa60
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F www/speed.tcl 656ed5be8cc9d536353e1a96927b925634a62933
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@ -306,7 +306,7 @@ F www/tclsqlite.tcl 3df553505b6efcad08f91e9b975deb2e6c9bb955
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F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
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F www/version3.tcl a99cf5f6d8bd4d5537584a2b342f0fb9fa601d8b
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F www/whentouse.tcl 97e2b5cd296f7d8057e11f44427dea8a4c2db513
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P 4c8d0a4c26e44088ffb9f21aa7641a5ebd0058be
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R 8c9dcafaf8c56c90363aaddb93c3711c
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P 0bbe73fccfe52700c2ae1122388764e81a78bc22
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R 116e86a3585b21a6c570826363946445
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U drh
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Z e855546ae219fc0150427c3e7e1f6fde
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Z 913c62cd31e3948a6b55fd91fd72e91a
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@ -1 +1 @@
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0bbe73fccfe52700c2ae1122388764e81a78bc22
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ccd12e9e790e271cb1dbbae1c13e9cb980eaf11d
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57
www/docs.tcl
57
www/docs.tcl
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# This script generates the "docs.html" page that describes various
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# sources of documentation available for SQLite.
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#
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set rcsid {$Id: docs.tcl,v 1.11 2005/03/19 14:45:50 drh Exp $}
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set rcsid {$Id: docs.tcl,v 1.12 2005/08/31 03:13:12 drh Exp $}
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source common.tcl
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header {SQLite Documentation}
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puts {
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@ -38,16 +38,17 @@ doc {SQL Syntax} {lang.html} {
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This document describes the SQL language that is understood by
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SQLite.
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}
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doc {Version 3 C/C++ API<br>Reference} {capi3ref.html} {
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This document describes each API function separately.
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}
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doc {Tcl API} {tclsqlite.html} {
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A description of the TCL interface bindings for SQLite.
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}
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doc {Pragma commands} {pragma.html} {
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This document describes SQLite performance tuning options and other
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special purpose database commands.
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}
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doc {Version 2 C/C++ API} {c_interface.html} {
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A description of the C/C++ interface bindings for SQLite through version
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2.8
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}
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doc {SQLite Version 3} {version3.html} {
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A summary of of the changes between SQLite version 2.8 and SQLite version 3.0.
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}
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@ -55,23 +56,6 @@ doc {Version 3 C/C++ API} {capi3.html} {
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A description of the C/C++ interface bindings for SQLite version 3.0.0
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and following.
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}
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doc {Version 3 C/C++ API<br>Reference} {capi3ref.html} {
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This document describes each API function separately.
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}
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doc {Tcl API} {tclsqlite.html} {
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A description of the TCL interface bindings for SQLite.
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}
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doc {Locking And Concurrency<br>In SQLite Version 3} {lockingv3.html} {
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A description of how the new locking code in version 3 increases
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concurrancy and decreases the problem of writer starvation.
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}
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doc {Version 2 DataTypes } {datatypes.html} {
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A description of how SQLite version 2 handles SQL datatypes.
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Short summary: Everything is a string.
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}
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doc {Version 3 DataTypes } {datatype3.html} {
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SQLite version 3 introduces the concept of manifest typing, where the
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type of a value is associated with the value itself, not the column that
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@ -79,10 +63,17 @@ doc {Version 3 DataTypes } {datatype3.html} {
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This page describes data typing for SQLite version 3 in further detail.
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}
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doc {Release History} {changes.html} {
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A chronology of SQLite releases going back to version 1.0.0
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doc {Locking And Concurrency<br>In SQLite Version 3} {lockingv3.html} {
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A description of how the new locking code in version 3 increases
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concurrancy and decreases the problem of writer starvation.
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}
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doc {Overview Of The Optimizer} {optoverview.html} {
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A quick overview of the various query optimizations that are
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attempted by the SQLite code generator.
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}
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doc {Null Handling} {nulls.html} {
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Different SQL database engines handle NULLs in different ways. The
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SQL standards are ambiguous. This document describes how SQLite handles
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@ -98,6 +89,22 @@ doc {Unsupported SQL} {omitted.html} {
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This page describes features of SQL that SQLite does not support.
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}
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doc {Version 2 C/C++ API} {c_interface.html} {
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A description of the C/C++ interface bindings for SQLite through version
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2.8
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}
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doc {Version 2 DataTypes } {datatypes.html} {
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A description of how SQLite version 2 handles SQL datatypes.
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Short summary: Everything is a string.
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}
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doc {Release History} {changes.html} {
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A chronology of SQLite releases going back to version 1.0.0
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}
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doc {Speed Comparison} {speed.html} {
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The speed of version 2.7.6 of SQLite is compared against PostgreSQL and
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MySQL.
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#
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# Run this TCL script to generate HTML for the goals.html file.
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#
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set rcsid {$Id: optoverview.tcl,v 1.1 2005/08/31 01:50:00 drh Exp $}
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set rcsid {$Id: optoverview.tcl,v 1.2 2005/08/31 03:13:12 drh Exp $}
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source common.tcl
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header {The SQLite Query Optimizer Overview}
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@ -58,7 +58,7 @@ HEADING 0 {The SQLite Query Optimizer Overview}
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PARAGRAPH {
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This document provides a terse overview of how the query optimizer
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for SQLite works. This is not a tutoral. Some prior knowledge of how
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for SQLite works. This is not a tutorial. Some prior knowledge of how
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database engines operate is likely needed in order to fully understand
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this text.
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}
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@ -411,7 +411,7 @@ PARAGRAPH {
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If, however, all columns that were to be fetched from the table are
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already available in the index itself, SQLite will use the values
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contained in the index and will never look up the original table
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row. This saves a binary search for each table and can make many
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row. This saves one binary search for each row and can make many
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queries run twice as fast.
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}
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@ -441,11 +441,48 @@ PARAGRAPH {
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To overcome this problem, SQLite attempts to flatten subqueries in
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the FROM clause of a SELECT.
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This involves inserting the FROM clause of the subquery into the
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FROM clause of the outer query and rewriting certain expressions in
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the outer query.
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There is a long list of conditions that must be met in order for
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query flattening to occur. These conditions are fully documented in
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source code comments in the select.c source file.
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FROM clause of the outer query and rewriting expressions in
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the outer query that refer to the result set of the subquery.
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For example:
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}
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CODE {
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SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5
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}
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PARAGRAPH {
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Would be rewritten using query flattening as:
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}
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CODE {
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SELECT x+y AS a FROM t1 WHERE z<100 AND a>5
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}
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PARAGRAPH {
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There is a long list of conditions that must all be met in order for
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query flattening to occur.
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}
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PARAGRAPH {
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<ol>
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<li> The subquery and the outer query do not both use aggregates.</li>
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<li> The subquery is not an aggregate or the outer query is not a join. </li>
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<li> The subquery is not the right operand of a left outer join, or
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the subquery is not itself a join. </li>
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<li> The subquery is not DISTINCT or the outer query is not a join. </li>
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<li> The subquery is not DISTINCT or the outer query does not use
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aggregates. </li>
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<li> The subquery does not use aggregates or the outer query is not
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DISTINCT. </li>
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<li> The subquery has a FROM clause. </li>
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<li> The subquery does not use LIMIT or the outer query is not a join. </li>
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<li> The subquery does not use LIMIT or the outer query does not use
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aggregates. </li>
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<li> The subquery does not use aggregates or the outer query does not
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use LIMIT. </li>
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<li> The subquery and the outer query do not both have ORDER BY clauses.</li>
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<li> The subquery is not the right term of a LEFT OUTER JOIN or the
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subquery has no WHERE clause. </li>
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</ol>
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}
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PARAGRAPH {
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The proof that query flattening may safely occur if all of the the
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above conditions are met is left as an exercise to the reader.
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}
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PARAGRAPH {
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Query flattening is an important optimization when views are used as
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@ -455,7 +492,7 @@ PARAGRAPH {
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HEADING 1 {The MIN/MAX optimization} minmax
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PARAGRAPH {
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Queries of the following forms will be optimized to run in logorithmic
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Queries of the following forms will be optimized to run in logarithmic
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time assuming appropriate indices exist:
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}
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CODE {
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@ -465,5 +502,7 @@ CODE {
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PARAGRAPH {
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In order for these optimizations to occur, they must appear in exactly
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the form shown above - changing only the name of the table and column.
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It is not permissible to add a WHERE clause or do any arithmetic on the
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result. The result set must contain a single column.
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And the column in the MIN or MAX function must be an indexed column.
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}
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