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

Artifact cdb47d01acc4a634a34fd25abe85189e0d0f1e62:


# 2012 September 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.
#
#***********************************************************************
#
# Tests for the optimization which attempts to use a covering index
# for a full-table scan (under the theory that the index will be smaller
# and require less I/O and hence will run faster.)
#

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

set testprefix coveridxscan

do_test 1.1 {
  db eval {
    CREATE TABLE t1(a,b,c);
    INSERT INTO t1 VALUES(5,4,3), (4,8,2), (3,2,1);
    CREATE INDEX t1ab ON t1(a,b);
    CREATE INDEX t1b ON t1(b);
    SELECT a FROM t1;
  }
  # covering index used for the scan, hence values are increasing
} {3 4 5}

do_test 1.2 {
  db eval {
    SELECT a, c FROM t1;
  }
  # There is no covering index, hence the values are in rowid order
} {5 3 4 2 3 1}

do_test 1.3 {
  db eval {
    SELECT b FROM t1;
  }
  # Choice of two indices: use the one with fewest columns
} {2 4 8}

do_test 2.1 {
  optimization_control db cover-idx-scan 0
  db eval {SELECT a FROM t1}
  # With the optimization turned off, output in rowid order
} {5 4 3}
do_test 2.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 2.3 {
  db eval {SELECT b FROM t1}
} {4 8 2}

db close
sqlite3_shutdown
sqlite3_config_cis 0
sqlite3 db test.db

do_test 3.1 {
  db eval {SELECT a FROM t1}
  # With the optimization configured off, output in rowid order
} {5 4 3}
do_test 3.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 3.3 {
  db eval {SELECT b FROM t1}
} {4 8 2}

db close
sqlite3_shutdown
sqlite3_config_cis 1
sqlite3 db test.db

# The CIS optimization is enabled again.  Covering indices are once again
# used for all table scans.
do_test 4.1 {
  db eval {SELECT a FROM t1}
} {3 4 5}
do_test 4.2 {
  db eval {SELECT a, c FROM t1}
} {5 3 4 2 3 1}
do_test 4.3 {
  db eval {SELECT b FROM t1}
} {2 4 8}


finish_test