Fix for bug #54575: crash when joining tables with unique set column(backport from 5.1)

Problem: a flaw (derefencing a NULL pointer) in the LIKE optimization
code may lead to a server crash in some rare cases.

Fix: check the pointer before its dereferencing.

mysql-test/r/func_like.result

@@ -165,3 +165,17 @@ select 'andre%' like 'andre
 select _cp1251'andre%' like convert('andre%' using cp1251)  escape '';
 _cp1251'andre%' like convert('andre%' using cp1251)  escape ''
 1
+End of 4.1 tests
+#
+# Bug #54575: crash when joining tables with unique set column
+#
+CREATE TABLE t1(a SET('a') NOT NULL, UNIQUE KEY(a));
+CREATE TABLE t2(b INT PRIMARY KEY);
+INSERT INTO t1 VALUES ();
+Warnings:
+Warning	1364	Field 'a' doesn't have a default value
+INSERT INTO t2 VALUES (1), (2), (3);
+SELECT 1 FROM t2 JOIN t1 ON 1 LIKE a GROUP BY a;
+1
+DROP TABLE t1, t2;
+End of 5.1 tests

mysql-test/t/func_like.test

@@ -112,5 +112,19 @@ select 'andre%' like 'andre
 #
 select _cp1251'andre%' like convert('andre%' using cp1251)  escape '';
 
-#
-# End of 4.1 tests
+
+--echo End of 4.1 tests
+
+
+--echo #
+--echo # Bug #54575: crash when joining tables with unique set column
+--echo #
+CREATE TABLE t1(a SET('a') NOT NULL, UNIQUE KEY(a));
+CREATE TABLE t2(b INT PRIMARY KEY);
+INSERT INTO t1 VALUES ();
+INSERT INTO t2 VALUES (1), (2), (3);
+SELECT 1 FROM t2 JOIN t1 ON 1 LIKE a GROUP BY a;
+DROP TABLE t1, t2;
+
+
+--echo End of 5.1 tests

sql/item_cmpfunc.cc

@@ -4220,13 +4220,14 @@ Item_func::optimize_type Item_func_like::select_optimize() const
   if (args[1]->const_item())
   {
     String* res2= args[1]->val_str((String *)&tmp_value2);
+    const char *ptr2;
 
-    if (!res2)
+    if (!res2 || !(ptr2= res2->ptr()))
       return OPTIMIZE_NONE;
 
-    if (*res2->ptr() != wild_many)
+    if (*ptr2 != wild_many)
     {
-      if (args[0]->result_type() != STRING_RESULT || *res2->ptr() != wild_one)
+      if (args[0]->result_type() != STRING_RESULT || *ptr2 != wild_one)
 	return OPTIMIZE_OP;
     }
   }