MDEV-16721: Assertion `ctx.compare_type_handler()->cmp_type() != STRING_RESULT'

failed

The bug appeared as in MDEV-12387 setup_jtbm_semi_joins() procedure had been
devided into two functions, one called before optimization of WHERE clause
and another after this optimization. When the second function was called for
a degenerated jtbm semi join equalities connecting the subselect and
the parent select were created but invocation of fix_fields() for these
equalities was missing.

mysql-test/main/in_subq_cond_pushdown.result

@@ -3802,3 +3802,15 @@ EXPLAIN
 }
 DROP TABLE t1,t2,t3;
 DROP VIEW v1,v2;
+#
+# MDEV-16721: IN-subquery defined with the AUTO-INCREMENT column
+#             and used with the ZEROFILL column
+#
+CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY);
+CREATE TABLE t2 (b INT ZEROFILL);
+INSERT INTO t2 VALUES (2), (3);
+SELECT *
+FROM t2
+WHERE t2.b IN (SELECT MIN(t1.a) from t1);
+b
+DROP TABLE t1, t2;

mysql-test/main/in_subq_cond_pushdown.test

@@ -757,3 +757,19 @@ EVAL EXPLAIN FORMAT=JSON $query;
 
 DROP TABLE t1,t2,t3;
 DROP VIEW v1,v2;
+
+--echo #
+--echo # MDEV-16721: IN-subquery defined with the AUTO-INCREMENT column
+--echo #             and used with the ZEROFILL column
+--echo #
+
+CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY);
+CREATE TABLE t2 (b INT ZEROFILL);
+
+INSERT INTO t2 VALUES (2), (3);
+
+SELECT *
+FROM t2
+WHERE t2.b IN (SELECT MIN(t1.a) from t1);
+
+DROP TABLE t1, t2;

sql/opt_subselect.cc

@@ -5738,7 +5738,8 @@ bool execute_degenerate_jtbm_semi_join(THD *thd,
         new (thd->mem_root) Item_func_eq(thd,
                                          subq_pred->left_expr->element_index(i),
                                          new_sink->row[i]);
-      if (!eq_cond || eq_list.push_back(eq_cond, thd->mem_root))
+      if (!eq_cond || eq_cond->fix_fields(thd, NULL) ||
+          eq_list.push_back(eq_cond, thd->mem_root))
         DBUG_RETURN(TRUE);
     }
   }