MDEV-29028 Queries using RANDOM_BYTES get stored in query cache

Mark the RANDOM_BYTES function as uncacheable.

mysql-test/main/query_cache.result

@@ -2239,3 +2239,28 @@ DROP TABLE t;
 restore defaults
 SET GLOBAL query_cache_type= default;
 SET GLOBAL query_cache_size=@save_query_cache_size;
+#
+# MDEV-29028: Queries using RANDOM_BYTES get stored in query cache
+#
+set @qcache= @@global.query_cache_type;
+set global query_cache_type= 1;
+set query_cache_type= 1;
+create table t1 (a int);
+insert into t1 values (1000);
+flush status;
+select * from information_schema.global_status where variable_name in ('Qcache_inserts','Qcache_hits') order by variable_name;
+VARIABLE_NAME	VARIABLE_VALUE
+QCACHE_HITS	0
+QCACHE_INSERTS	0
+select * from information_schema.global_status where variable_name in ('Qcache_inserts','Qcache_hits') order by variable_name;
+VARIABLE_NAME	VARIABLE_VALUE
+QCACHE_HITS	0
+QCACHE_INSERTS	0
+select random_bytes(1024) = random_bytes(1024) as improbable;
+improbable
+0
+drop table t1;
+set global query_cache_type= @qcache;
+#
+# End of 10.10 tests
+#

mysql-test/main/query_cache.test

@@ -1834,3 +1834,35 @@ DROP TABLE t;
 --echo restore defaults
 SET GLOBAL query_cache_type= default;
 SET GLOBAL query_cache_size=@save_query_cache_size;
+
+--echo #
+--echo # MDEV-29028: Queries using RANDOM_BYTES get stored in query cache
+--echo #
+
+set @qcache= @@global.query_cache_type;
+set global query_cache_type= 1;
+set query_cache_type= 1;
+
+create table t1 (a int);
+insert into t1 values (1000);
+
+flush status;
+--let $v1 = `select hex(random_bytes(a)) from t1`
+select * from information_schema.global_status where variable_name in ('Qcache_inserts','Qcache_hits') order by variable_name;
+
+--let $v2 = `select hex(random_bytes(a)) from t1`
+select * from information_schema.global_status where variable_name in ('Qcache_inserts','Qcache_hits') order by variable_name;
+
+if ($v1 == $v2) {
+--echo highly improbable $v1 = $v2
+}
+
+select random_bytes(1024) = random_bytes(1024) as improbable;
+
+# Cleanup
+drop table t1;
+set global query_cache_type= @qcache;
+
+--echo #
+--echo # End of 10.10 tests
+--echo #

sql/item_create.cc

@@ -5003,6 +5003,7 @@ Create_func_random_bytes Create_func_random_bytes::s_singleton;
 Item *Create_func_random_bytes::create_1_arg(THD *thd, Item *arg1)
 {
   thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
+  thd->lex->uncacheable(UNCACHEABLE_RAND);
   return new (thd->mem_root) Item_func_random_bytes(thd, arg1);
 }