MDEV-24089 support oracle syntax: rownum

The ROWNUM() function is for SELECT mapped to JOIN->accepted_rows, which is incremented for each accepted rows. For Filesort, update, insert, delete and load data, we map ROWNUM() to internal variables incremented when the table is changed. The connection between the row counter and Item_func_rownum is done in sql_select.cc::fix_items_after_optimize() and sql_insert.cc::fix_rownum_pointers() When ROWNUM() is used anywhere in query, the optimization to ignore ORDER BY in sub queries are disabled. This was done to get the following common Oracle query to work: select * from (select * from t1 order by a desc) as t where rownum() <= 2; MDEV-3926 "Wrong result with GROUP BY ... WITH ROLLUP" contains a discussion about this topic. LIMIT optimization is enabled when in a top level WHERE clause comparing ROWNUM() with a numerical constant using any of the following expressions: - ROWNUM() < # - ROWNUM() <= # - ROWNUM() = 1 ROWNUM() can be also be the right argument to the comparison function. LIMIT optimization is done in two cases: - For the current sub query when the ROWNUM comparison is done on the top level: SELECT * from t1 WHERE rownum() <= 2 AND t1.a > 0 - For an inner sub query, when the upper level has only a ROWNUM comparison in the WHERE clause: SELECT * from (select * from t1) as t WHERE rownum() <= 2 In Oracle mode, one can also use ROWNUM without parentheses. Other things: - Fixed bug where the optimizer tries to optimize away sub queries with RAND_TABLE_BIT set (non-deterministic queries). Now these sub queries will not be converted to joins. This bug fix was also needed to get rownum() working inside subqueries. - In remove_const() remove setting simple_order to FALSE if ROLLUP is USED. This code was disable a long time ago because of wrong assignment in the following code. Instead we set simple_order to false if RAND_TABLE_BIT was used in the SELECT list. This ensures that we don't delete ORDER BY if the result set is not deterministic, like in 'SELECT RAND() AS 'r' FROM t1 ORDER BY r'; - Updated parameters for Sort_param::init_for_filesort() to be able to provide filesort with information where the number of accepted rows should be stored - Reordered fields in class Filesort to optimize storage layout - Added new error messsage to tell that a function can't be used in HAVING - Added field 'with_rownum' to THD to mark that ROWNUM() is used in the query. Co-author: Oleksandr Byelkin <sanja@mariadb.com> LIMIT optimization for sub query

Author: montywi

mysql-test/main/derived_view.result

@@ -2698,7 +2698,7 @@ ON p.id = g.p_random
 ORDER BY gallery_name ASC 
 ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	10	Using filesort
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	10	Using temporary; Using filesort
 1	PRIMARY	p	eq_ref	PRIMARY	PRIMARY	4	g.p_random	1	Using where
 2	DERIVED	gal	ALL	NULL	NULL	NULL	NULL	10
 3	DEPENDENT SUBQUERY	pi	ref	gallery_id	gallery_id	4	test.gal.id	4	Using temporary; Using filesort

mysql-test/main/having.result

@@ -837,13 +837,15 @@ ANALYZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	analyze	status	Engine-independent statistics collected
 test.t1	analyze	status	OK
-SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t)
-GROUP BY t HAVING r = 1 ORDER BY t1.u;
+explain SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1 ORDER BY t1.u;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	8	Using temporary; Using filesort
+SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1 ORDER BY t1.u;
 t	r
 10	1
 12	1
-151
-171
+141
+161
 DROP TABLE t1;
 DROP FUNCTION next_seq_value;
 DROP TABLE series;

mysql-test/main/having.test

@@ -884,8 +884,8 @@ CREATE TABLE t1 (t INT, u INT, KEY(t));
 INSERT INTO t1 VALUES(10, 10), (11, 11), (12, 12), (12, 13),(14, 15), (15, 16),
  (16, 17), (17, 17);
 ANALYZE TABLE t1;
-SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t)
-  GROUP BY t HAVING r = 1 ORDER BY t1.u;
+explain SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1 ORDER BY t1.u;
+SELECT t, next_seq_value() r FROM t1 FORCE INDEX(t) GROUP BY t HAVING r = 1 ORDER BY t1.u;
 
 DROP TABLE t1;
 DROP FUNCTION next_seq_value;