3 files changed, 39 insertions, 2 deletions
diff --git a/mysql-test/main/opt_trace.result b/mysql-test/main/opt_trace.result
index 2eef0da62bb..a8277070438 100644
--- a/mysql-test/main/opt_trace.result
+++ b/mysql-test/main/opt_trace.result
@@ -8522,5 +8522,22 @@ SELECT a FROM t1 WHERE (a,b) in (SELECT @c,@d);
 a
 DROP TABLE t1;
 #
+# MDEV-30334 Optimizer trace produces invalid JSON with WHERE subquery
+#  Simple code rearrangement to stop it displaying an unsigned int in a String.
+#
+SET optimizer_trace= 'enabled=on';
+CREATE TABLE t1 (id INT PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (3),(4);
+SELECT * FROM t1 WHERE id < ( SELECT SUM(a) FROM t2 );
+id
+1
+2
+SELECT JSON_VALID(trace) FROM information_schema.optimizer_trace;
+JSON_VALID(trace)
+1
+DROP TABLE t1, t2;
+#
 # End of 10.4 tests
 #
diff --git a/mysql-test/main/opt_trace.test b/mysql-test/main/opt_trace.test
index 0785d828a07..1bc48b6f75a 100644
--- a/mysql-test/main/opt_trace.test
+++ b/mysql-test/main/opt_trace.test
@@ -678,5 +678,22 @@ SELECT a FROM t1 WHERE (a,b) in (SELECT @c,@d);
 DROP TABLE t1;
 
 --echo #
+--echo # MDEV-30334 Optimizer trace produces invalid JSON with WHERE subquery
+--echo #  Simple code rearrangement to stop it displaying an unsigned int in a String.
+--echo #
+
+SET optimizer_trace= 'enabled=on';
+ 
+CREATE TABLE t1 (id INT PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (a INT);
+INSERT INTO t2 VALUES (3),(4);
+ 
+SELECT * FROM t1 WHERE id < ( SELECT SUM(a) FROM t2 );
+SELECT JSON_VALID(trace) FROM information_schema.optimizer_trace;
+ 
+DROP TABLE t1, t2;
+
+--echo #
 --echo # End of 10.4 tests
 --echo #
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index eb54484fa51..228ce799457 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -27865,6 +27865,8 @@ void st_select_lex::print(THD *thd, String *str, enum_query_type query_type)
       }
     }
     str->append(" */ ");
+    if (join && join->cleaned) // if this join has been cleaned
+      return;                  // the select_number printed above is all we have
   }
 
   str->append(STRING_WITH_LEN("select "));
@@ -27875,11 +27877,12 @@ void st_select_lex::print(THD *thd, String *str, enum_query_type query_type)
       JOIN already cleaned up so it is dangerous to print items
       because temporary tables they pointed on could be freed.
     */
-    str->append('#');
-    str->append(select_number);
+    str->append("#");
+    str->append_ulonglong(select_number);
     return;
   }
 
+
   /* First add options */
   if (options & SELECT_STRAIGHT_JOIN)
     str->append(STRING_WITH_LEN("straight_join "));