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

Artifact a3be0d1a53a7d2edff208a5e442312957047e972:


# 2014-06-17
#
# 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.
#
#*************************************************************************
#
# This file implements regression tests for SQLite library.  The
# focus of this script is testing automatic index creation logic,
# and specifically that an automatic index will not be created that
# shadows a declared index.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix autoindex3

# The t1b and t2d indexes are not very selective.  It used to be that
# the autoindex mechanism would create automatic indexes on t1(b) or
# t2(d), make assumptions that they were reasonably selective, and use
# them instead of t1b or t2d.  But that would be cheating, because the
# automatic index cannot be any more selective than the real index.
#
# This test verifies that the cheat is no longer allowed.
#
do_execsql_test autoindex3-100 {
  CREATE TABLE t1(a,b,x);
  CREATE TABLE t2(c,d,y);
  CREATE INDEX t1b ON t1(b);
  CREATE INDEX t2d ON t2(d);
  ANALYZE sqlite_master;
  INSERT INTO sqlite_stat1 VALUES('t1','t1b','10000 500');
  INSERT INTO sqlite_stat1 VALUES('t2','t2d','10000 500');
  ANALYZE sqlite_master;
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d=b;
} {~/AUTO/}

# Automatic indexes can still be used if existing indexes do not
# participate in == constraints.
#
do_execsql_test autoindex3-110 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d>b AND x=y;
} {/AUTO/}
do_execsql_test autoindex3-120 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d<b AND x=y;
} {/AUTO/}
do_execsql_test autoindex3-130 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IS NULL AND x=y;
} {/AUTO/}
do_execsql_test autoindex3-140 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IN (5,b) AND x=y;
} {/AUTO/}

reset_db
do_execsql_test 210 {
  CREATE TABLE v(b, d, e);
  CREATE TABLE u(a, b, c);
  ANALYZE sqlite_master;
  INSERT INTO "sqlite_stat1" VALUES('u','uab','40000 400 1');
  INSERT INTO "sqlite_stat1" VALUES('v','vbde','40000 400 1 1');
  INSERT INTO "sqlite_stat1" VALUES('v','ve','40000 21');

  CREATE INDEX uab on u(a, b);
  CREATE INDEX ve on v(e);
  CREATE INDEX vbde on v(b,d,e);

  DROP TABLE IF EXISTS sqlite_stat4;
  ANALYZE sqlite_master;
}

# At one point, SQLite was using the inferior plan:
#
#   0|0|1|SEARCH TABLE v USING INDEX ve (e>?)
#   0|1|0|SEARCH TABLE u USING COVERING INDEX uab (ANY(a) AND b=?)
#
# on the basis that the real index "uab" must be better than the automatic
# index. This is not right - a skip-scan is not necessarily better than an
# automatic index scan.
#
do_eqp_test 220 {
  select count(*) from u, v where u.b = v.b and v.e > 34;
} {
  0 0 1 {SEARCH TABLE v USING INDEX ve (e>?)} 
  0 1 0 {SEARCH TABLE u USING AUTOMATIC COVERING INDEX (b=?)}
}


finish_test