Apply fix by Roy Lyseng:

Bug#48623: Multiple subqueries are optimized incorrectly
      
The function setup_semijoin_dups_elimination() has a major loop that
goes through every table in the JOIN object. Usually, there is a normal
"plus one" increment in the for loop that implements this, but each semijoin
nest is treated as one entity and there is another increment that skips past
the semijoin nest to the next table in the JOIN object. However, when
combining these two increments, the next joined table is skipped, and if that
happens to be the start of another semijoin nest, the correct processing
for that nest will not be carried out.

mysql-test/r/subselect_sj.result:
  Added test results for bug#48623
mysql-test/r/subselect_sj_jcl6.result:
  Added test results for bug#48623
mysql-test/t/subselect_sj.test:
  Added test case for bug#48623
sql/opt_subselect.cc:
  Omitted the "plus one" increment in the for loop, added "plus one"
  in the remaining switch case, fixed coding style issue in remaining
  increment operations.

mysql-test/r/subselect_sj.result

@@ -1079,3 +1079,36 @@ execute stmt;
 partner_id
 partner2
 drop table t1,t2,t3,t4;
+# 
+# Bug#48623 Multiple subqueries are optimized incorrectly
+# 
+CREATE TABLE t1(val VARCHAR(10));
+CREATE TABLE t2(val VARCHAR(10));
+CREATE TABLE t3(val VARCHAR(10));
+INSERT INTO t1  VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t2 VALUES('aaa'), ('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t3 VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+EXPLAIN
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+AND t1.val IN (SELECT t3.val FROM t3
+WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	5	
+1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	5	Using where; FirstMatch(t1)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; FirstMatch(t3)
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+AND t1.val IN (SELECT t3.val FROM t3
+WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
+val
+aaa
+eee
+DROP TABLE t1;
+DROP TABLE t2;
+DROP TABLE t3;
+# End of Bug#48623

mysql-test/r/subselect_sj_jcl6.result

@@ -1084,6 +1084,39 @@ partner_id
 partner2
 drop table t1,t2,t3,t4;
 # 
+# Bug#48623 Multiple subqueries are optimized incorrectly
+# 
+CREATE TABLE t1(val VARCHAR(10));
+CREATE TABLE t2(val VARCHAR(10));
+CREATE TABLE t3(val VARCHAR(10));
+INSERT INTO t1  VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t2 VALUES('aaa'), ('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t3 VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+EXPLAIN
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+AND t1.val IN (SELECT t3.val FROM t3
+WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	5	
+1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	5	Using where; FirstMatch(t1); Using join buffer
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; FirstMatch(t3); Using join buffer
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+AND t1.val IN (SELECT t3.val FROM t3
+WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
+val
+aaa
+eee
+DROP TABLE t1;
+DROP TABLE t2;
+DROP TABLE t3;
+# End of Bug#48623
+#
 # BUG#49129: Wrong result with IN-subquery with join_cache_level=6 and firstmatch=off
 #
 CREATE TABLE t0 (a INT);

mysql-test/t/subselect_sj.test

@@ -943,5 +943,35 @@ execute stmt;
 execute stmt;
 drop table t1,t2,t3,t4;
 
+--echo # 
+--echo # Bug#48623 Multiple subqueries are optimized incorrectly
+--echo # 
+
+CREATE TABLE t1(val VARCHAR(10));
+CREATE TABLE t2(val VARCHAR(10));
+CREATE TABLE t3(val VARCHAR(10));
+
+INSERT INTO t1  VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t2 VALUES('aaa'), ('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+INSERT INTO t3 VALUES('aaa'), ('bbb'), ('eee'), ('mmm'), ('ppp');
+
+EXPLAIN
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+                 WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+  AND t1.val IN (SELECT t3.val FROM t3
+                 WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
+
+SELECT *
+FROM t1
+WHERE t1.val IN (SELECT t2.val FROM t2
+                 WHERE  t2.val LIKE 'a%' OR t2.val LIKE 'e%')
+  AND t1.val IN (SELECT t3.val FROM t3
+                 WHERE  t3.val LIKE 'a%' OR t3.val LIKE 'e%');
 
+DROP TABLE t1;
+DROP TABLE t2;
+DROP TABLE t3;
 
+--echo # End of Bug#48623

sql/opt_subselect.cc

@@ -3030,7 +3030,7 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
   THD *thd= join->thd;
   DBUG_ENTER("setup_semijoin_dups_elimination");
 
-  for (i= join->const_tables ; i < join->tables ; i++)
+  for (i= join->const_tables ; i < join->tables; )
   {
     JOIN_TAB *tab=join->join_tab + i;
     POSITION *pos= join->best_positions + i;
@@ -3039,7 +3039,7 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
       case SJ_OPT_MATERIALIZE:
       case SJ_OPT_MATERIALIZE_SCAN:
         /* Do nothing */
-        i += pos->n_sj_tables;
+        i+= pos->n_sj_tables;
         break;
       case SJ_OPT_LOOSE_SCAN:
       {
@@ -3055,7 +3055,7 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
         tab->loosescan_key_len= keylen;
         if (pos->n_sj_tables > 1) 
           tab[pos->n_sj_tables - 1].do_firstmatch= tab;
-        i += pos->n_sj_tables;
+        i+= pos->n_sj_tables;
         break;
       }
       case SJ_OPT_DUPS_WEEDOUT:
@@ -3152,7 +3152,7 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
         join->join_tab[first_table].flush_weedout_table= sjtbl;
         join->join_tab[i + pos->n_sj_tables - 1].check_weed_out_table= sjtbl;
 
-        i += pos->n_sj_tables;
+        i+= pos->n_sj_tables;
         break;
       }
       case SJ_OPT_FIRST_MATCH:
@@ -3174,10 +3174,11 @@ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options,
           }
         }
         j[-1].do_firstmatch= jump_to;
-        i += pos->n_sj_tables;
+        i+= pos->n_sj_tables;
         break;
       }
       case SJ_OPT_NONE:
+        i++;
         break;
     }
   }