MWL#17: Table elimination

- add debug tests (were accidentally not pushed with the bulk of WL)

mysql-test/r/table_elim_debug.result

+drop table if exists t1, t2;
+create table t1 (a int);
+insert into t1 values (0),(1),(2),(3);
+create table t2 (a int primary key, b int) 
+as select a, a as b from t1 where a in (1,2);
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
+set optimizer_switch='table_elimination=off';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	Using index
+set optimizer_switch='table_elimination=on';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
+set optimizer_switch='table_elimination=default';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
+drop table t1, t2;

mysql-test/t/table_elim_debug.test

+#
+# Table elimination (MWL#17) tests that need debug build
+#
+--source include/have_debug.inc
+
+--disable_warnings
+drop table if exists t1, t2;
+--enable_warnings
+
+# Check if optimizer_switch works
+
+create table t1 (a int);
+insert into t1 values (0),(1),(2),(3);
+
+create table t2 (a int primary key, b int) 
+  as select a, a as b from t1 where a in (1,2);
+
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+
+set optimizer_switch='table_elimination=off';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+set optimizer_switch='table_elimination=on';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+set optimizer_switch='table_elimination=default';
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+
+drop table t1, t2;