test/index8.test

# 2016-07-27
#
# 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 ORDER BY and LIMIT on an index scan.
#


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

# Performance regression reported at
# http://www.mail-archive.com/sqlite-users@mailinglists.sqlite.org/msg98615.html
#
# Caused by the ORDER BY LIMIT optionation for check-in
# https://sqlite.org/src/info/bf46179d44843769
#
# Fixed on approximately 2016-07-27 by changes that compute a better score
# for index scans by taking into account WHERE clause constraints that can
# be handled by the index and do not require a table lookup.
#
do_execsql_test 1.0 {
  CREATE TABLE t1(a,b,c,d);
  WITH RECURSIVE c(x) AS (VALUES(0) UNION ALL SELECT x+1 FROM c WHERE x<100)
  INSERT INTO t1(a,b,c,d)
     SELECT x/10, x%10, x%19, x FROM c;
  CREATE INDEX t1abc ON t1(a,b,c);
  SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2;
} {0 4 4 4 2 3 4 23}

# Prior to the fix, the following EQP would show a table scan and a sort
# rather than an index scan.
#
do_execsql_test 1.0eqp {
  EXPLAIN QUERY PLAN
  SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2;
} {/SCAN TABLE t1 USING INDEX t1abc/}

# If we change the index so that it no longer covers the WHERE clause,
# then we should (correctly) revert to using a table scan.
#
do_execsql_test 1.1 {
  DROP INDEX t1abc;
  CREATE INDEX t1abd ON t1(a,b,d);
  SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2;
} {0 4 4 4 2 3 4 23}
do_execsql_test 1.1eqp {
  EXPLAIN QUERY PLAN
  SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2;
} {~/USING INDEX/}


finish_test