gitlab.com/CoiaPrant/sqlite3@v1.19.1/testdata/tcl/index8.test (about) 1 # 2016-07-27 2 # 3 # The author disclaims copyright to this source code. In place of 4 # a legal notice, here is a blessing: 5 # 6 # May you do good and not evil. 7 # May you find forgiveness for yourself and forgive others. 8 # May you share freely, never taking more than you give. 9 # 10 #*********************************************************************** 11 # 12 # Test cases for ORDER BY and LIMIT on an index scan. 13 # 14 15 16 set testdir [file dirname $argv0] 17 source $testdir/tester.tcl 18 19 # Performance regression reported at 20 # http://www.mail-archive.com/sqlite-users@mailinglists.sqlite.org/msg98615.html 21 # 22 # Caused by the ORDER BY LIMIT optionation for check-in 23 # https://sqlite.org/src/info/bf46179d44843769 24 # 25 # Fixed on approximately 2016-07-27 by changes that compute a better score 26 # for index scans by taking into account WHERE clause constraints that can 27 # be handled by the index and do not require a table lookup. 28 # 29 do_execsql_test 1.0 { 30 CREATE TABLE t1(a,b,c,d); 31 WITH RECURSIVE c(x) AS (VALUES(0) UNION ALL SELECT x+1 FROM c WHERE x<100) 32 INSERT INTO t1(a,b,c,d) 33 SELECT x/10, x%10, x%19, x FROM c; 34 CREATE INDEX t1abc ON t1(a,b,c); 35 SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2; 36 } {0 4 4 4 2 3 4 23} 37 38 # Prior to the fix, the following EQP would show a table scan and a sort 39 # rather than an index scan. 40 # 41 do_execsql_test 1.0eqp { 42 EXPLAIN QUERY PLAN 43 SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2; 44 } {/SCAN t1 USING INDEX t1abc/} 45 46 # If we change the index so that it no longer covers the WHERE clause, 47 # then we should (correctly) revert to using a table scan. 48 # 49 do_execsql_test 1.1 { 50 DROP INDEX t1abc; 51 CREATE INDEX t1abd ON t1(a,b,d); 52 SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2; 53 } {0 4 4 4 2 3 4 23} 54 do_execsql_test 1.1eqp { 55 EXPLAIN QUERY PLAN 56 SELECT * FROM t1 WHERE c=4 ORDER BY a, b LIMIT 2; 57 } {~/USING INDEX/} 58 59 60 finish_test