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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

Artifact 5b2ba0dbe8074aa13e416b37c753991f0a2492d7:


# 2012 November 9
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# 
# Test cases for query planning decisions.


#
# The tests in this file demonstrate the behaviour of the query planner
# in determining the order in which joined tables are scanned.
#
# Assume there are two tables being joined - t1 and t2. Each has a cost
# if it is the outer loop, and a cost if it is the inner loop. As follows:
#
#   t1(outer) - cost of scanning t1 as the outer loop.
#   t1(inner) - cost of scanning t1 as the inner loop.
#   t2(outer) - cost of scanning t2 as the outer loop.
#   t2(inner) - cost of scanning t2 as the inner loop.
#
# Depending on the order in which the planner nests the scans, the total
# cost of the join query is one of:
#
#   t1(outer) * t2(inner)
#   t2(outer) * t1(inner)
#
# The tests in this file attempt to verify that the planner nests joins in
# the correct order when the following are true:
#
#   + (t1(outer) * t2(inner)) > (t1(inner) * t2(outer)
#   +  t1(outer) < t2(outer)
#
# In other words, when the best overall query plan has t2 as the outer loop,
# but when the outer loop is considered independent of the inner, t1 is the
# most efficient choice.
#
# In order to make them more predictable, automatic indexes are turned off for
# the tests in this file.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix whereF

do_execsql_test 1.0 {
  PRAGMA automatic_index = 0;
  CREATE TABLE t1(a, b, c);
  CREATE TABLE t2(d, e, f);
  CREATE UNIQUE INDEX i1 ON t1(a);
  CREATE UNIQUE INDEX i2 ON t2(d);
} {}

foreach {tn sql} {
  1 "SELECT * FROM t1,           t2 WHERE t1.a=t2.e AND t2.d<t1.b AND t1.c!=10"
  2 "SELECT * FROM t2,           t1 WHERE t1.a=t2.e AND t2.d<t1.b AND t1.c!=10"
  3 "SELECT * FROM t2 CROSS JOIN t1 WHERE t1.a=t2.e AND t2.d<t1.b AND t1.c!=10"
} {
  do_test 1.$tn {
    db eval "EXPLAIN QUERY PLAN $sql"
   } {/.*SCAN TABLE t2\y.*SEARCH TABLE t1\y.*/}
}

do_execsql_test 2.0 {
  DROP TABLE t1;
  DROP TABLE t2;
  CREATE TABLE t1(a, b, c);
  CREATE TABLE t2(d, e, f);

  CREATE UNIQUE INDEX i1 ON t1(a);
  CREATE UNIQUE INDEX i2 ON t1(b);
  CREATE UNIQUE INDEX i3 ON t2(d);
} {}

foreach {tn sql} {
  1 "SELECT * FROM t1,           t2 WHERE t1.a>? AND t2.d>t1.c AND t1.b=t2.e"
  2 "SELECT * FROM t2,           t1 WHERE t1.a>? AND t2.d>t1.c AND t1.b=t2.e"
  3 "SELECT * FROM t2 CROSS JOIN t1 WHERE t1.a>? AND t2.d>t1.c AND t1.b=t2.e"
} {
  do_test 2.$tn {
    db eval "EXPLAIN QUERY PLAN $sql"
   } {/.*SCAN TABLE t2\y.*SEARCH TABLE t1\y.*/}
}

do_execsql_test 3.0 {
  DROP TABLE t1;
  DROP TABLE t2;
  CREATE TABLE t1(a, b, c);
  CREATE TABLE t2(d, e, f);

  CREATE UNIQUE INDEX i1 ON t1(a, b);
  CREATE INDEX i2 ON t2(d);
} {}

foreach {tn sql} {
  1 {SELECT t1.a, t1.b, t2.d, t2.e FROM t1, t2 
     WHERE t2.d=t1.b AND t1.a=(t2.d+1) AND t1.b = (t2.e+1)}

  2 {SELECT t1.a, t1.b, t2.d, t2.e FROM t2, t1 
     WHERE t2.d=t1.b AND t1.a=(t2.d+1) AND t1.b = (t2.e+1)}

  3 {SELECT t1.a, t1.b, t2.d, t2.e FROM t2 CROSS JOIN t1 
     WHERE t2.d=t1.b AND t1.a=(t2.d+1) AND t1.b = (t2.e+1)}
} {
  do_test 3.$tn {
    db eval "EXPLAIN QUERY PLAN $sql"
   } {/.*SCAN TABLE t2\y.*SEARCH TABLE t1\y.*/}
}

do_execsql_test 4.0 {
  CREATE TABLE t4(a,b,c,d,e, PRIMARY KEY(a,b,c));
  CREATE INDEX t4adc ON t4(a,d,c);
  CREATE UNIQUE INDEX t4aebc ON t4(a,e,b,c);
  EXPLAIN QUERY PLAN SELECT rowid FROM t4 WHERE a=? AND b=?;
} {/a=. AND b=./}

finish_test