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# 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 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
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