Bug #30277189: EXPLAIN ANALYZE + MULTI-TABLE JOIN = CRASH

Fix an assertion failure when doing EXPLAIN ANALYZE on a query that
the iterator executor doesn't support.

Change-Id: I10bb3d58afe49155bf06972afaeed5f6eb68f248

Author: Steinar H. Gunderson

mysql-test/r/explain_tree.result

@@ -748,6 +748,23 @@ EXPLAIN
 
 DROP TABLE t1;
 CREATE TABLE t1 (
+c1 INTEGER,
+c2 INTEGER
+);
+CREATE TABLE t2 (
+c1 INTEGER,
+c2 INTEGER
+);
+CREATE TABLE t3 (
+c1 INTEGER,
+c2 INTEGER
+);
+set optimizer_switch='block_nested_loop=on';
+EXPLAIN ANALYZE SELECT * FROM t1 JOIN t2 ON t1.c1 = t2.c2 JOIN t3 ON t2.c2 > t3.c2;
+ERROR 42000: This version of MySQL doesn't yet support 'EXPLAIN ANALYZE on this query'
+set optimizer_switch='block_nested_loop=off';
+DROP TABLE t1, t2, t3;
+CREATE TABLE t1 (
 b INTEGER,
 UNIQUE KEY ix1 (b)
 );

mysql-test/t/explain_tree.test

@@ -428,6 +428,25 @@ EXPLAIN FORMAT=tree SELECT * FROM t1, ( SELECT f1 FROM t1 UNION ALL SELECT f1 +
 
 DROP TABLE t1;
 
+# EXPLAIN ANALYZE on a query the iterator executor doesn't support should give an error.
+CREATE TABLE t1 (
+  c1 INTEGER,
+  c2 INTEGER
+);
+CREATE TABLE t2 (
+  c1 INTEGER,
+  c2 INTEGER
+);
+CREATE TABLE t3 (
+  c1 INTEGER,
+  c2 INTEGER
+);
+set optimizer_switch='block_nested_loop=on';
+--error ER_NOT_SUPPORTED_YET
+EXPLAIN ANALYZE SELECT * FROM t1 JOIN t2 ON t1.c1 = t2.c2 JOIN t3 ON t2.c2 > t3.c2;
+set optimizer_switch='block_nested_loop=off';
+DROP TABLE t1, t2, t3;
+
 #
 # Bug #30220791: INCORRECT RESULT WHEN THE ITERATOR EXECUTOR IS USED
 #

sql/opt_explain.cc

@@ -2205,6 +2205,13 @@ bool explain_query(THD *explain_thd, const THD *query_thd,
         unit->set_executed();
         return true;
       }
+      if (unit->root_iterator() == nullptr) {
+        // TODO(sgunders): Remove when the iterator executor supports
+        // all queries.
+        my_error(ER_NOT_SUPPORTED_YET, MYF(0), "EXPLAIN ANALYZE on this query");
+        unit->set_executed();
+        return true;
+      }
 
       // Run the query, but with the result suppressed.
       Query_result_null null_result;