diff --git a/mysql-test/r/join.result b/mysql-test/r/join.result
index d1234ecbd56..8dff149e1ef 100644
--- a/mysql-test/r/join.result
+++ b/mysql-test/r/join.result
@@ -1117,6 +1117,23 @@ ON t4.a = t5.a
 ON t1.a = t3.a;
 a	a	a	a	a	a
 DROP TABLE t1,t2,t3,t4,t5,t6;
+#
+# Bug#48483: crash in get_best_combination()
+#
+CREATE TABLE t1(f1 INT);
+INSERT INTO t1 VALUES (1),(2);
+CREATE VIEW v1 AS SELECT 1 FROM t1 LEFT JOIN t1 AS t2 on 1=1;
+EXPLAIN EXTENDED
+SELECT 1 FROM v1 right join v1 AS v2 ON RAND();
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1003	select 1 AS `1` from `test`.`t1` left join `test`.`t1` `t2` on((1 = 1)) left join (`test`.`t1` left join `test`.`t1` `t2` on((1 = 1))) on(rand()) where 1
+DROP VIEW v1;
+DROP TABLE t1;
 End of 5.0 tests.
 CREATE TABLE t1 (f1 int);
 CREATE TABLE t2 (f1 int);
diff --git a/mysql-test/r/loaddata.result b/mysql-test/r/loaddata.result
index 5e25132880f..93782d624ed 100644
--- a/mysql-test/r/loaddata.result
+++ b/mysql-test/r/loaddata.result
@@ -484,4 +484,15 @@ SET character_set_filesystem=default;
 select @@character_set_filesystem;
 @@character_set_filesystem
 binary
+#
+# Bug #51850: crash/memory overlap when using load data infile and set 
+#  col equal to itself!
+#
+CREATE TABLE t1(col0 LONGBLOB);
+SELECT 'test' INTO OUTFILE 't1.txt';
+LOAD DATA INFILE 't1.txt' IGNORE INTO TABLE t1 SET col0=col0;
+SELECT * FROM t1;
+col0
+test
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/t/join.test b/mysql-test/t/join.test
index 761121313e5..c1b35b51563 100644
--- a/mysql-test/t/join.test
+++ b/mysql-test/t/join.test
@@ -784,6 +784,18 @@ FROM
 
 DROP TABLE t1,t2,t3,t4,t5,t6;
 
+--echo #
+--echo # Bug#48483: crash in get_best_combination()
+--echo #
+
+CREATE TABLE t1(f1 INT);
+INSERT INTO t1 VALUES (1),(2);
+CREATE VIEW v1 AS SELECT 1 FROM t1 LEFT JOIN t1 AS t2 on 1=1;
+EXPLAIN EXTENDED
+SELECT 1 FROM v1 right join v1 AS v2 ON RAND();
+DROP VIEW v1;
+DROP TABLE t1;
+
 --echo End of 5.0 tests.
 
 
diff --git a/mysql-test/t/loaddata.test b/mysql-test/t/loaddata.test
index 7bfe2491c7c..a32fee6b46e 100644
--- a/mysql-test/t/loaddata.test
+++ b/mysql-test/t/loaddata.test
@@ -532,5 +532,19 @@ SET character_set_filesystem=default;
 select @@character_set_filesystem;
 
 
+--echo #
+--echo # Bug #51850: crash/memory overlap when using load data infile and set 
+--echo #  col equal to itself!
+--echo #
+
+CREATE TABLE t1(col0 LONGBLOB);
+SELECT 'test' INTO OUTFILE 't1.txt';
+LOAD DATA INFILE 't1.txt' IGNORE INTO TABLE t1 SET col0=col0;
+SELECT * FROM t1;
+
+DROP TABLE t1;
+let $MYSQLD_DATADIR= `select @@datadir`;
+remove_file $MYSQLD_DATADIR/test/t1.txt;
+
 
 --echo End of 5.1 tests
diff --git a/sql/item.cc b/sql/item.cc
index 9a685c80c18..183868ea5c6 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5295,14 +5295,22 @@ int Item_field::save_in_field(Field *to, bool no_conversions)
   if (result_field->is_null())
   {
     null_value=1;
-    res= set_field_to_null_with_conversions(to, no_conversions);
+    return set_field_to_null_with_conversions(to, no_conversions);
   }
-  else
+  to->set_notnull();
+
+  /*
+    If we're setting the same field as the one we're reading from there's 
+    nothing to do. This can happen in 'SET x = x' type of scenarios.
+  */  
+  if (to == result_field)
   {
-    to->set_notnull();
-    res= field_conv(to,result_field);
     null_value=0;
+    return 0;
   }
+
+  res= field_conv(to,result_field);
+  null_value=0;
   return res;
 }
 
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 3a62396b880..56102779771 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -5145,6 +5145,11 @@ greedy_search(JOIN      *join,
     if (best_extension_by_limited_search(join, remaining_tables, idx, record_count,
                                          read_time, search_depth, prune_level))
       DBUG_RETURN(TRUE);
+    /*
+      'best_read < DBL_MAX' means that optimizer managed to find
+      some plan and updated 'best_positions' array accordingly.
+    */
+    DBUG_ASSERT(join->best_read < DBL_MAX); 
 
     if (size_remain <= search_depth)
     {
@@ -8925,8 +8930,14 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
           we still make the inner tables dependent on the outer tables.
           It would be enough to set dependency only on one outer table
           for them. Yet this is really a rare case.
+          Note:
+          RAND_TABLE_BIT mask should not be counted as it
+          prevents update of inner table dependences.
+          For example it might happen if RAND() function
+          is used in JOIN ON clause.
 	*/  
-        if (!(prev_table->on_expr->used_tables() & ~prev_used_tables))
+        if (!((prev_table->on_expr->used_tables() & ~RAND_TABLE_BIT) &
+              ~prev_used_tables))
           prev_table->dep_tables|= used_tables;
       }
     }