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

Artifact 42af58de25a6436502e43006e9e59e2d71bcb0cf:


# 2014-10-04
#
# 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.
# This file implements tests for the ANALYZE command.
#

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

ifcapable {!stat4} {
  finish_test
  return
}


# Set up a table with the following properties:
#
#    * Contains 1000 rows.
#    * Column a contains even integers between 0 and 18, inclusive (so that
#      a=? for any such integer matches 100 rows).
#    * Column b contains integers between 0 and 9, inclusive.
#    * Column c contains integers between 0 and 199, inclusive (so that
#      for any such integer, c=? matches 5 rows).
#    * Then add 7 rows with a new value for "a" - 3001. The stat4 table will
#      not contain any samples with a=3001.
#
do_execsql_test 1.0 {
  CREATE TABLE t1(a, b, c);
}
do_test 1.1 {
  for {set i 1} {$i < 1000} {incr i} {
    set c [expr $i % 200]
    execsql { INSERT INTO t1(a, b, c) VALUES( 2*($i/100), $i%10, $c ) }
  }

  execsql {
    INSERT INTO t1 VALUES(3001, 3001, 3001);
    INSERT INTO t1 VALUES(3001, 3001, 3002);
    INSERT INTO t1 VALUES(3001, 3001, 3003);
    INSERT INTO t1 VALUES(3001, 3001, 3004);
    INSERT INTO t1 VALUES(3001, 3001, 3005);
    INSERT INTO t1 VALUES(3001, 3001, 3006);
    INSERT INTO t1 VALUES(3001, 3001, 3007);

    CREATE INDEX t1_ab ON t1(a, b);
    CREATE INDEX t1_c ON t1(c);

    ANALYZE;
  }
} {}

# With full ANALYZE data, SQLite sees that c=150 (5 rows) is better than
# a=3001 (7 rows).
#
do_eqp_test 1.2 {
  SELECT * FROM t1 WHERE a=3001 AND c=150;
} {
  0 0 0 {SEARCH TABLE t1 USING INDEX t1_c (c=?)}
}

do_test 1.3 {
  execsql { DELETE FROM sqlite_stat1 }
  db close
  sqlite3 db test.db
} {}

# Without stat1, because 3001 is larger than all samples in the stat4
# table, SQLite thinks that a=3001 matches just 1 row. So it (incorrectly)
# chooses it over the c=150 index (5 rows). Even with stat1 data, things
# worked this way before commit [e6f7f97dbc].
#
do_eqp_test 1.4 {
  SELECT * FROM t1 WHERE a=3001 AND c=150;
} {
  0 0 0 {SEARCH TABLE t1 USING INDEX t1_ab (a=?)}
}

do_test 1.5 {
  execsql { 
    UPDATE t1 SET a=13 WHERE a = 3001;
    ANALYZE;
  }
} {}

do_eqp_test 1.6 {
  SELECT * FROM t1 WHERE a=13 AND c=150;
} {
  0 0 0 {SEARCH TABLE t1 USING INDEX t1_c (c=?)}
}

do_test 1.7 {
  execsql { DELETE FROM sqlite_stat1 }
  db close
  sqlite3 db test.db
} {}

# Same test as 1.4, except this time the 7 rows that match the a=? condition 
# do not feature larger values than all rows in the stat4 table. So SQLite
# gets this right, even without stat1 data.
do_eqp_test 1.8 {
  SELECT * FROM t1 WHERE a=13 AND c=150;
} {
  0 0 0 {SEARCH TABLE t1 USING INDEX t1_c (c=?)}
}

finish_test