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| 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 TABLE 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 |
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