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diff --git a/mysql-test/main/table_elim.test b/mysql-test/main/table_elim.test
new file mode 100644
index 00000000000..8de4743b9fd
--- /dev/null
+++ b/mysql-test/main/table_elim.test
@@ -0,0 +1,643 @@
+#
+# Table elimination (MWL#17) tests
+#
+--disable_warnings
+drop table if exists t0, t1, t2, t3, t4, t5, t6;
+drop view if exists v1, v2;
+--enable_warnings
+
+SET @save_optimizer_switch=@@optimizer_switch;
+SET optimizer_switch='outer_join_with_cache=off';
+
+create table t1 (a int);
+insert into t1 values (0),(1),(2),(3);
+create table t0 as select * from t1;
+
+create table t2 (a int primary key, b int) 
+  as select a, a as b from t1 where a in (1,2);
+
+create table t3 (a int primary key, b int) 
+  as select a, a as b from t1 where a in (1,3);
+
+--echo # This will be  eliminated:
+explain select t1.a from t1 left join t2 on t2.a=t1.a;
+explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
+
+select t1.a from t1 left join t2 on t2.a=t1.a;
+
+--echo # This will not be eliminated as t2.b is in in select list:
+explain select * from t1 left join t2 on t2.a=t1.a;
+
+--echo # This will not be eliminated as t2.b is in in order list:
+explain select t1.a from t1 left join t2 on t2.a=t1.a order by t2.b;
+
+--echo # This will not be eliminated as t2.b is in group list:
+explain select t1.a from t1 left join t2 on t2.a=t1.a group by t2.b;
+
+--echo # This will not be eliminated as t2.b is in the WHERE
+explain select t1.a from t1 left join t2 on t2.a=t1.a where t2.b < 3 or t2.b is null;
+
+--echo # Elimination of multiple tables:
+explain select t1.a from t1 left join (t2 join t3) on t2.a=t1.a and t3.a=t1.a;
+
+--echo # Elimination of multiple tables (2):
+explain select t1.a from t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and t3.a=t1.a;
+
+--echo # Elimination when done within an outer join nest:
+explain extended
+select t0.*
+from
+  t0 left join (t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
+  t3.a=t1.a) on t0.a=t1.a;
+
+--echo # Elimination with aggregate functions
+explain select count(*) from t1 left join t2 on t2.a=t1.a;
+explain select count(1) from t1 left join t2 on t2.a=t1.a;
+explain select count(1) from t1 left join t2 on t2.a=t1.a group by t1.a;
+
+--echo This must not use elimination:
+explain select count(1) from t1 left join t2 on t2.a=t1.a group by t2.a;
+
+drop table t0, t1, t2, t3;
+
+# This will stand for elim_facts
+create table t0 ( id integer, primary key (id));
+
+# Attribute1, non-versioned
+create table t1 (
+  id integer,
+  attr1 integer,
+  primary key (id),
+  key (attr1)
+);
+
+# Attribute2, time-versioned
+create table t2 (
+  id integer,
+  attr2 integer,
+  fromdate date,
+  primary key (id, fromdate),
+  key (attr2,fromdate)
+);
+
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+insert into t0 select A.id + 10*B.id from t0 A, t0 B where B.id > 0;
+
+insert into t1 select id, id from t0;
+insert into t2 select id, id, date_add('2009-06-22', interval id day) from t0;
+insert into t2 select id, id+1, date_add('2008-06-22', interval id day) from t0;
+
+create view v1 as
+select 
+  f.id, a1.attr1, a2.attr2
+from 
+  t0 f 
+  left join t1 a1 on a1.id=f.id
+  left join t2 a2 on a2.id=f.id and 
+                     a2.fromdate=(select MAX(fromdate) from
+                                  t2 where id=a2.id);
+create view v2 as
+select 
+  f.id, a1.attr1, a2.attr2
+from 
+  t0 f 
+  left join t1 a1 on a1.id=f.id
+  left join t2 a2 on a2.id=f.id and 
+                     a2.fromdate=(select MAX(fromdate) from
+                                  t2 where id=f.id);
+
+--echo This should use one table:
+explain select id from v1 where id=2;
+--echo This should use one table:
+explain extended select id from v1 where id in (1,2,3,4);
+--echo This should use facts and a1 tables:
+explain extended select id from v1 where attr1 between 12 and 14;
+--echo This should use facts, a2 and its subquery:
+explain extended select id from v1 where attr2 between 12 and 14;
+
+# Repeat for v2: 
+
+--echo This should use one table:
+explain select id from v2 where id=2;
+--echo This should use one table:
+explain extended select id from v2 where id in (1,2,3,4);
+--echo This should use facts and a1 tables:
+explain extended select id from v2 where attr1 between 12 and 14;
+--echo This should use facts, a2 and its subquery:
+explain extended select id from v2 where attr2 between 12 and 14;
+
+drop view v1, v2;
+drop table t0, t1, t2;
+
+#
+# Tests for the code that uses t.keypartX=func(t.keypartY) equalities to
+# make table elimination inferences
+#
+create table t1 (a int);
+insert into t1 values (0),(1),(2),(3);
+
+create table t2 (pk1 int, pk2 int, pk3 int, col int, primary key(pk1, pk2, pk3));
+insert into t2 select a,a,a,a from t1;
+
+--echo This must use only t1:
+explain select t1.* from t1 left join t2 on t2.pk1=t1.a and 
+                                            t2.pk2=t2.pk1+1 and
+                                            t2.pk3=t2.pk2+1;
+
+--echo This must use only t1:
+explain select t1.* from t1 left join t2 on t2.pk1=t1.a and 
+                                            t2.pk3=t2.pk1+1 and
+                                            t2.pk2=t2.pk3+1;
+
+--echo This must use both:
+explain select t1.* from t1 left join t2 on t2.pk1=t1.a and 
+                                            t2.pk3=t2.pk1+1 and
+                                            t2.pk2=t2.pk3+t2.col;
+
+--echo This must use only t1:
+explain select t1.* from t1 left join t2 on t2.pk2=t1.a and 
+                                            t2.pk1=t2.pk2+1 and
+                                            t2.pk3=t2.pk1;
+
+drop table t1, t2;
+#
+# Check that equality propagation is taken into account
+#
+create table t1 (pk int primary key, col int);
+insert into t1 values (1,1),(2,2);
+
+create table t2 like t1;
+insert into t2 select * from t1;
+
+create table t3 like t1;
+insert into t3 select * from t1;
+
+explain 
+select t1.* from t1 left join ( t2 left join t3 on t3.pk=t2.col) on t2.col=t1.col;
+
+explain 
+select t1.*, t2.* from t1 left join (t2 left join t3 on t3.pk=t2.col) on t2.pk=t1.col;
+
+explain select t1.* 
+from 
+  t1 left join ( t2 left join t3 on t3.pk=t2.col or t3.pk=t2.col) 
+  on t2.col=t1.col or t2.col=t1.col;
+
+explain select t1.*, t2.* 
+from 
+  t1 left join 
+  (t2 left join t3 on t3.pk=t2.col or t3.pk=t2.col) 
+  on t2.pk=t1.col or t2.pk=t1.col;
+
+drop table t1, t2, t3;
+
+--echo # 
+--echo # Check things that look like functional dependencies but really are not
+--echo # 
+
+create table t1 (a char(10) character set latin1 collate latin1_general_ci primary key);
+insert into t1 values ('foo');
+insert into t1 values ('bar');
+
+create table t2 (a char(10) character set latin1 collate latin1_general_cs primary key);
+insert into t2 values ('foo');
+insert into t2 values ('FOO');
+
+-- echo this must not use table elimination:
+explain select t1.* from t1 left join t2 on t2.a='foo' collate latin1_general_ci; 
+
+-- echo this must not use table elimination:
+explain select t1.* from t1 left join t2 on t2.a=t1.a collate latin1_general_ci; 
+drop table t1,t2;
+
+create table t1 (a int primary key);
+insert into t1 values (1),(2);
+create table t2 (a char(10) primary key);
+insert into t2 values ('1'),('1.0');
+-- echo this must not use table elimination:
+explain select t1.* from t1 left join t2 on t2.a=1;
+-- echo this must not use table elimination:
+explain select t1.* from t1 left join t2 on t2.a=t1.a;
+
+drop table t1, t2;
+# partial unique keys do not work at the moment, although they are able to
+# provide one-match guarantees:
+create table t1 (a char(10) primary key);
+insert into t1 values ('foo'),('bar');
+
+create table t2 (a char(10), unique key(a(2)));
+insert into t2 values
+  ('foo'),('bar'),('boo'),('car'),('coo'),('par'),('doo'),('tar');
+
+explain select t1.* from t1 left join t2 on t2.a=t1.a;
+
+drop table t1, t2;
+
+--echo #
+--echo # check UPDATE/DELETE that look like they could be eliminated
+--echo #
+create table t1 (a int primary key, b int);
+insert into t1 values (1,1),(2,2),(3,3);
+
+create table t2 like t1;
+insert into t2 select * from t1;
+update t1 left join t2 using (a) set t2.a=t2.a+100;
+select * from t1;
+select * from t2;
+
+delete from t2;
+insert into t2 select * from t1;
+
+delete t2 from t1 left join t2 using (a);
+select * from t1;
+select * from t2;
+drop table t1, t2;
+
+--echo #
+--echo # Tests with various edge-case ON expressions
+--echo #
+create table t1 (a int, b int, c int, d int);
+insert into t1 values (0,0,0,0),(1,1,1,1),(2,2,2,2),(3,3,3,3);
+
+create table t2 (pk int primary key, b int) 
+  as select a as pk, a as b from t1 where a in (1,2);
+
+create table t3 (pk1 int, pk2 int, b int, unique(pk1,pk2));
+insert into t3 select a as pk1, a as pk2, a as b from t1 where a in (1,3);
+
+explain select t1.a from t1 left join t2 on t2.pk=t1.a and t2.b<t1.b;
+explain select t1.a from t1 left join t2 on t2.pk=t1.a or t2.b<t1.b;
+explain select t1.a from t1 left join t2 on t2.b<t1.b or t2.pk=t1.a;
+
+explain select t1.a from t1 left join t2 on t2.pk between 10 and 20;
+explain select t1.a from t1 left join t2 on t2.pk between 0.5 and 1.5;
+explain select t1.a from t1 left join t2 on t2.pk between 10 and 10;
+
+explain select t1.a from t1 left join t2 on t2.pk in (10);
+explain select t1.a from t1 left join t2 on t2.pk in (t1.a);
+
+explain select t1.a from t1 left join t2 on TRUE;
+
+explain select t1.a from t1 left join t3 on t3.pk1=t1.a and t3.pk2 IS NULL;
+
+drop table t1,t2,t3;
+
+--echo #
+--echo # Multi-equality tests 
+--echo #
+create table t1 (a int, b int, c int, d int);
+insert into t1 values (0,0,0,0),(1,1,1,1),(2,2,2,2),(3,3,3,3);
+
+create table t2 (pk int primary key, b int, c int);
+insert into t2 select a,a,a from t1 where a in (1,2);
+
+explain 
+select t1.* 
+from t1 left join t2 on t2.pk=t2.c and t2.b=t1.a and t1.a=t1.b and t2.c=t2.b
+where t1.d=1;
+
+explain 
+select t1.* 
+from 
+    t1 
+  left join 
+    t2 
+  on (t2.pk=t2.c and t2.b=t1.a and t1.a=t1.b and t2.c=t2.b) or
+     (t2.pk=t2.c and t2.b=t1.a and t1.a=t1.b and t2.c=t2.b) 
+where t1.d=1;
+
+--echo #This can't be eliminated:
+explain 
+select t1.* 
+from 
+    t1 
+  left join 
+    t2 
+  on (t2.pk=t2.c and t2.b=t1.a and               t2.c=t1.b) or
+     (t2.pk=t2.c and               t1.a=t1.b and t2.c=t1.b) 
+where t1.d=1;
+
+explain 
+select t1.* 
+from 
+    t1 
+  left join 
+    t2 
+  on (t2.pk=t2.c and t2.b=t1.a and t2.c=t1.b) or
+     (t2.pk=t2.c and               t2.c=t1.b) 
+;
+
+explain 
+select t1.* 
+from t1 left join t2 on t2.pk=3 or t2.pk= 4;
+
+explain 
+select t1.* 
+from t1 left join t2 on t2.pk=3 or t2.pk= 3;
+
+explain 
+select t1.* 
+from t1 left join t2 on (t2.pk=3 and t2.b=3) or (t2.pk= 4 and t2.b=3);
+
+drop table t1, t2;
+
+--echo #
+--echo # LPBUG#523593: Running RQG optimizer_no_subquery crashes MariaDB
+--echo #
+
+CREATE TABLE t1 (
+  `pk` int(11) NOT NULL AUTO_INCREMENT,
+  `col_int_nokey` int(11) DEFAULT NULL,
+  `col_int_key` int(11) DEFAULT NULL,
+  `col_date_key` date DEFAULT NULL,
+  `col_date_nokey` date DEFAULT NULL,
+  `col_time_key` time DEFAULT NULL,
+  `col_time_nokey` time DEFAULT NULL,
+  `col_datetime_key` datetime DEFAULT NULL,
+  `col_datetime_nokey` datetime DEFAULT NULL,
+  `col_varchar_key` varchar(1) DEFAULT NULL,
+  `col_varchar_nokey` varchar(1) DEFAULT NULL,
+  PRIMARY KEY (`pk`),
+  KEY `col_int_key` (`col_int_key`),
+  KEY `col_date_key` (`col_date_key`),
+  KEY `col_time_key` (`col_time_key`),
+  KEY `col_datetime_key` (`col_datetime_key`),
+  KEY `col_varchar_key` (`col_varchar_key`,`col_int_key`)
+);
+CREATE TABLE t2 LIKE t1;
+
+INSERT INTO t1 VALUES 
+ (10,7,8,NULL,NULL,'01:27:35','01:27:35','2002-02-26 06:14:37','2002-02-26 06:14:37','v','v'),
+ (11,1,9,'2006-06-14','2006-06-14','19:48:31','19:48:31','1900-01-01 00:00:00','1900-01-01 00:00:00','r','r');
+INSERT INTO t2 SELECT * FROM t1;
+
+SELECT table2.col_int_key AS field1 
+FROM ( 
+  t2 AS table1 
+  RIGHT OUTER JOIN 
+  ( 
+    ( t1 AS table2 STRAIGHT_JOIN 
+      t1 AS table3 ON (
+               (table3.col_varchar_nokey = table2.col_varchar_key ) AND 
+               (table3.pk = table2.col_int_key)) 
+    )
+  ) ON 
+    (
+      (table3.col_varchar_key = table2.col_varchar_key) OR 
+      (table3.col_int_key = table2.pk)
+    )
+)
+HAVING field1 < 216;
+
+DROP TABLE t1, t2;
+
+
+--echo #
+--echo # LPBUG#524025 Running RQG outer_join test leads to crash
+--echo #
+
+CREATE TABLE t0 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY (pk)
+);
+
+CREATE TABLE t1 (
+  col_int int(11) DEFAULT NULL,
+  col_int_key int(11) DEFAULT NULL,
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  col_varchar_10_latin1 varchar(10) DEFAULT NULL,
+  PRIMARY KEY (pk)
+);
+INSERT INTO t1 VALUES (5,5,1,'t'), (NULL,NULL,2,'y');
+
+CREATE TABLE t2 (
+  col_int int(11) DEFAULT NULL
+);
+INSERT INTO t2 VALUES (8), (4);
+
+CREATE TABLE t3 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  PRIMARY KEY (pk)
+);
+INSERT INTO t3 VALUES (1),(8);
+
+CREATE TABLE t4 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  col_varchar_1024_latin1_key varchar(1024) DEFAULT NULL,
+  col_int int(11) DEFAULT NULL,
+  PRIMARY KEY (pk)
+);
+INSERT INTO t4 VALUES (1,'o',1), (2,'w',2);
+
+CREATE TABLE t5 (
+  col_varchar_1024_utf8_key varchar(1024) CHARACTER SET utf8 DEFAULT NULL,
+  col_varchar_1024_latin1_key varchar(1024) DEFAULT NULL,
+  col_varchar_10_utf8_key varchar(1024) CHARACTER SET utf8 DEFAULT NULL,
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  col_int_key int(11) DEFAULT NULL,
+  PRIMARY KEY (pk)
+);
+INSERT INTO t5 VALUES ('k','a','z',1,2),('x','a','w',2,7);
+
+CREATE TABLE t6 (
+  col_int int(11) DEFAULT NULL,
+  col_int_key int(11) DEFAULT NULL
+);
+INSERT INTO t6 VALUES (6,1),(8,3);
+ 
+SELECT
+  table3.col_int AS field1,
+  table1.col_int AS field2,
+  table1.col_int_key AS field3,
+  table1.pk AS field4,
+  table1.col_int AS field5,
+  table2.col_int AS field6
+FROM
+  t1 AS table1
+  LEFT OUTER JOIN
+  t4 AS table2
+  LEFT JOIN t6 AS table3
+  RIGHT JOIN t3 AS table4
+  LEFT JOIN t5 AS table5 ON table4.pk = table5.pk
+  LEFT JOIN t0 AS table6 ON table5.col_int_key = table6.pk
+  ON table3.col_int_key = table5.pk
+  ON table2.col_varchar_1024_latin1_key = table5.col_varchar_10_utf8_key
+  LEFT JOIN t6 AS table7 ON table2.pk = table7.col_int
+  ON table1.col_varchar_10_latin1 = table5.col_varchar_1024_latin1_key
+  LEFT JOIN t2 AS table8 ON table3.col_int = table8.col_int
+WHERE
+  table1.col_int_key < table2.pk
+HAVING
+  field4 != 6;
+
+drop table t0,t1,t2,t3,t4,t5,t6;
+
+--echo #
+--echo # BUG#675118: Elimination of a table results in an invalid execution plan
+--echo #
+CREATE TABLE t1 (f1 int(11), PRIMARY KEY (f1)) ;
+
+CREATE TABLE t2 (f4 varchar(1024), KEY (f4)) ;
+INSERT IGNORE INTO t2 VALUES ('xcddwntkbxyorzdv'),
+   ('cnxxcddwntkbxyor'),('r'),('r'), ('did'),('I'),('when'),
+   ('hczkfqjeggivdvac'),('e'),('okay'),('up');
+
+CREATE TABLE t3 (f4 varchar(1024), f1 int(11), f2 int(11)) ;
+INSERT IGNORE INTO t3 VALUES ('f','4','0'),('n','5','-996540416');
+
+CREATE TABLE t4 (f1 int(11), f3 varchar(10)) ;
+INSERT IGNORE INTO t4 VALUES ('8','n'),('9','nwzcerzsgx'),('10','c');
+
+CREATE TABLE t5 (f5 int(11), KEY (f5)) ;
+
+EXPLAIN 
+SELECT t3.f2
+FROM t2
+LEFT JOIN t3
+LEFT JOIN t4
+LEFT JOIN t1 ON t4.f1 = t1.f1
+JOIN t5 ON t4.f3 ON t3.f1 = t5.f5 ON t2.f4 = t3.f4
+WHERE t3.f2 ;
+--echo # ^^ The above must not produce a QEP of t3,t5,t2,t4
+--echo #    as that violates the "no interleaving of outer join nests" rule.
+
+DROP TABLE t1,t2,t3,t4,t5;
+
+--echo #
+--echo # BUG#997747: Assertion `join->best_read < ((double)1.79..5e+308L)' 
+--echo #             failed in greedy_search with LEFT JOINs and unique keys  
+--echo #
+CREATE TABLE t1 (a1 INT);
+CREATE TABLE t2 (b1 INT);
+CREATE TABLE t3 (c1 INT, UNIQUE KEY(c1));
+CREATE TABLE t4 (d1 INT, UNIQUE KEY(d1));
+CREATE TABLE t5 (e1 INT);
+
+INSERT INTO t1 VALUES (1),(2);
+INSERT INTO t2 VALUES (2),(3);
+INSERT INTO t3 VALUES (3),(4);
+INSERT INTO t4 VALUES (4),(5);
+INSERT INTO t5 VALUES (5),(6);
+
+SELECT a1 FROM t1 LEFT JOIN t2 LEFT JOIN t3 LEFT JOIN t4
+ON c1 = d1 ON d1 = b1 ON a1 = b1
+LEFT JOIN t5 ON a1 = e1 ;
+
+DROP TABLE t1,t2,t3,t4,t5;
+
+--echo #
+--echo # BUG#884184: Wrong result with RIGHT JOIN + derived_merge
+--echo #
+CREATE TABLE t1 (a int(11), b varchar(1)) ;
+INSERT IGNORE INTO t1 VALUES (0,'g');
+
+CREATE TABLE t3 ( a varchar(1)) ;
+INSERT IGNORE INTO t3 VALUES ('g');
+
+CREATE TABLE t2 ( a int(11) NOT NULL, PRIMARY KEY (a));
+INSERT INTO t2 VALUES (9), (10);
+create view v1 as SELECT t1.* FROM t1 LEFT JOIN t2 ON ( t1.a = t2.a ) WHERE t2.a <> 0;
+
+SELECT alias1.* FROM t3 LEFT JOIN v1 as alias1 ON ( t3.a = alias1.b );
+EXPLAIN SELECT alias1.* FROM t3 LEFT JOIN v1 as alias1 ON ( t3.a = alias1.b );
+drop view v1;
+DROP TABLE t1,t2,t3;
+
+--echo #
+--echo # MDEV-5344: LEFT OUTER JOIN table data is lost in ON DUPLICATE KEY UPDATE section
+--echo #
+create table t1 (
+	id int(10) unsigned NOT NULL DEFAULT '0',
+	v int(10) unsigned DEFAULT '0',
+	PRIMARY KEY (id)
+);
+
+create table t2 (
+	id int(10) unsigned NOT NULL DEFAULT '0',
+	PRIMARY KEY (id)
+) ;
+
+create table t3 (
+	id int(10) unsigned NOT NULL DEFAULT '0',
+	v int(10) unsigned DEFAULT '0',
+	PRIMARY KEY (id)
+);
+
+insert into t1 values (1, 10), (2, 10);
+insert into t2 values (1), (2);
+insert into t3 values (1, 20);
+
+insert into t1 
+select t2.id, 5 from t2 LEFT OUTER JOIN t3 ON t2.id = t3.id
+on duplicate key update t1.v = t3.v;
+
+select * from t1;
+drop table t1,t2,t3;
+
+--echo #
+--echo # BUG#919878: Assertion `!eliminated_tables...
+--echo #
+CREATE TABLE t1 ( a INT );
+INSERT INTO t1 VALUES (1);
+
+CREATE TABLE t2
+  ( b INT, UNIQUE INDEX(b) );
+INSERT INTO t2 VALUES (1),(2);
+
+EXPLAIN EXTENDED
+  SELECT * FROM t2
+  WHERE b IN (
+    SELECT SUM(a) FROM t1 LEFT JOIN t2 ON b=a
+  );
+
+DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-4840: Wrong result (missing rows) on LEFT JOIN with InnoDB tables
+--echo #
+CREATE TABLE t1 (alpha3 VARCHAR(3));
+INSERT INTO t1 VALUES ('USA'),('CAN');
+
+CREATE TABLE t2 ( t3_code VARCHAR(3), name VARCHAR(64));
+INSERT INTO t2 VALUES ('USA','Austin'),('USA','Boston');
+
+CREATE TABLE t3 ( code VARCHAR(3),  name VARCHAR(64),  PRIMARY KEY (code),  UNIQUE KEY (name));
+INSERT INTO t3 VALUES ('CAN','Canada'),('USA','United States');
+
+SELECT *         FROM t1 LEFT JOIN ( t2 LEFT JOIN t3 ON t2.t3_code  = t3.code ) ON t1.alpha3 = t3.code;
+SELECT t1.alpha3 FROM t1 LEFT JOIN ( t2 LEFT JOIN t3 ON t2.t3_code  = t3.code ) ON t1.alpha3 = t3.code;
+
+DROP TABLE t1, t2, t3;
+
+SET optimizer_switch=@save_optimizer_switch;
+
+--echo #
+--echo # MDEV-7893: table_elimination works wrong with on computed expression and compound unique key
+--echo #  (just a testcase)
+CREATE TABLE t1 (
+  PostID int(10) unsigned NOT NULL
+) DEFAULT CHARSET=utf8;
+
+INSERT INTO t1 (PostID) VALUES (1), (2);
+
+CREATE TABLE t2 (
+  VoteID int(10) unsigned NOT NULL PRIMARY KEY AUTO_INCREMENT,
+  EntityID int(10) unsigned NOT NULL,
+  UserID int(10) unsigned NOT NULL,
+  UNIQUE KEY EntityID (EntityID,UserID)
+) DEFAULT CHARSET=utf8;
+  
+INSERT INTO t2 (EntityID, UserID) VALUES (1,  30), (2, 30);
+
+SELECT t1.*, T.Voted as Voted
+FROM 
+t1 LEFT JOIN (
+  SELECT 1 AS Voted, EntityID 
+  FROM t2 
+  WHERE t2.UserID = '20' ) AS T 
+  ON T.EntityID = t1.PostID
+WHERE t1.PostID='1'
+LIMIT 1;
+
+DROP TABLE t1,t2;
+