Fixed bug #15106.

A typo bug caused loss of a predicate of the form field=const in some cases.

mysql-test/r/select.result

@@ -3291,3 +3291,49 @@ f1	f2	x1
 30	1	30
 drop table t1;
 drop view v1, v2, v3;
+CREATE TABLE t1(key_a int4 NOT NULL, optimus varchar(32), PRIMARY KEY(key_a));
+CREATE TABLE t2(key_a int4 NOT NULL, prime varchar(32), PRIMARY KEY(key_a));
+CREATE table t3(key_a int4 NOT NULL, key_b int4 NOT NULL, foo varchar(32),
+PRIMARY KEY(key_a,key_b));
+INSERT INTO t1 VALUES (0,'');
+INSERT INTO t1 VALUES (1,'i');
+INSERT INTO t1 VALUES (2,'j');
+INSERT INTO t1 VALUES (3,'k');
+INSERT INTO t2 VALUES (1,'r');
+INSERT INTO t2 VALUES (2,'s');
+INSERT INTO t2 VALUES (3,'t');
+INSERT INTO t3 VALUES (1,5,'x');
+INSERT INTO t3 VALUES (1,6,'y');
+INSERT INTO t3 VALUES (2,5,'xx');
+INSERT INTO t3 VALUES (2,6,'yy');
+INSERT INTO t3 VALUES (2,7,'zz');
+INSERT INTO t3 VALUES (3,5,'xxx');
+SELECT t2.key_a,foo 
+FROM t1 INNER JOIN t2 ON t1.key_a = t2.key_a
+INNER JOIN t3 ON t1.key_a = t3.key_a
+WHERE t2.key_a=2 and key_b=5;
+key_a	foo
+2	xx
+EXPLAIN SELECT t2.key_a,foo 
+FROM t1 INNER JOIN t2 ON t1.key_a = t2.key_a
+INNER JOIN t3 ON t1.key_a = t3.key_a
+WHERE t2.key_a=2 and key_b=5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	8	const,const	1	
+SELECT t2.key_a,foo 
+FROM t1 INNER JOIN t2 ON t2.key_a = t1.key_a
+INNER JOIN t3 ON t1.key_a = t3.key_a
+WHERE t2.key_a=2 and key_b=5;
+key_a	foo
+2	xx
+EXPLAIN SELECT t2.key_a,foo 
+FROM t1 INNER JOIN t2 ON t2.key_a = t1.key_a
+INNER JOIN t3 ON t1.key_a = t3.key_a
+WHERE t2.key_a=2 and key_b=5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	SIMPLE	t2	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	8	const,const	1	
+DROP TABLE t1,t2,t3;

mysql-test/t/select.test

@@ -2760,3 +2760,48 @@ select f1, f2, v2.f1 as x1 from v2 order by v2.f1;
 select f1, f2, v3.f1 as x1 from v3 order by v3.f1;
 drop table t1;
 drop view v1, v2, v3;
+
+#
+# Bug #15106: lost equality predicate of the form field=const in a join query
+#
+
+CREATE TABLE t1(key_a int4 NOT NULL, optimus varchar(32), PRIMARY KEY(key_a));
+CREATE TABLE t2(key_a int4 NOT NULL, prime varchar(32), PRIMARY KEY(key_a));
+CREATE table t3(key_a int4 NOT NULL, key_b int4 NOT NULL, foo varchar(32),
+                PRIMARY KEY(key_a,key_b));
+
+INSERT INTO t1 VALUES (0,'');
+INSERT INTO t1 VALUES (1,'i');
+INSERT INTO t1 VALUES (2,'j');
+INSERT INTO t1 VALUES (3,'k');
+
+INSERT INTO t2 VALUES (1,'r');
+INSERT INTO t2 VALUES (2,'s');
+INSERT INTO t2 VALUES (3,'t');
+
+INSERT INTO t3 VALUES (1,5,'x');
+INSERT INTO t3 VALUES (1,6,'y');
+INSERT INTO t3 VALUES (2,5,'xx');
+INSERT INTO t3 VALUES (2,6,'yy');
+INSERT INTO t3 VALUES (2,7,'zz');
+INSERT INTO t3 VALUES (3,5,'xxx');
+
+SELECT t2.key_a,foo 
+  FROM t1 INNER JOIN t2 ON t1.key_a = t2.key_a
+          INNER JOIN t3 ON t1.key_a = t3.key_a
+    WHERE t2.key_a=2 and key_b=5;
+EXPLAIN SELECT t2.key_a,foo 
+  FROM t1 INNER JOIN t2 ON t1.key_a = t2.key_a
+          INNER JOIN t3 ON t1.key_a = t3.key_a
+    WHERE t2.key_a=2 and key_b=5;
+
+SELECT t2.key_a,foo 
+  FROM t1 INNER JOIN t2 ON t2.key_a = t1.key_a
+          INNER JOIN t3 ON t1.key_a = t3.key_a
+    WHERE t2.key_a=2 and key_b=5;
+EXPLAIN SELECT t2.key_a,foo 
+  FROM t1 INNER JOIN t2 ON t2.key_a = t1.key_a
+          INNER JOIN t3 ON t1.key_a = t3.key_a
+    WHERE t2.key_a=2 and key_b=5;
+
+DROP TABLE t1,t2,t3;

sql/item_cmpfunc.cc

@@ -3662,7 +3662,7 @@ void Item_equal::merge(Item_equal *item)
       the multiple equality already contains a constant and its 
       value is  not equal to the value of c.
     */
-    add(const_item);
+    add(c);
   }
   cond_false|= item->cond_false;
 }