3 files changed, 35 insertions, 2 deletions
diff --git a/mysql-test/suite/innodb/r/foreign_key.result b/mysql-test/suite/innodb/r/foreign_key.result
index bd40f98ef65..2facbccc466 100644
--- a/mysql-test/suite/innodb/r/foreign_key.result
+++ b/mysql-test/suite/innodb/r/foreign_key.result
@@ -755,4 +755,17 @@ DROP TABLE t1;
 CREATE TABLE t1 (a GEOMETRY, INDEX(a(8)),
 FOREIGN KEY (a) REFERENCES x (xx)) ENGINE=InnoDB;
 ERROR HY000: Can't create table `test`.`t1` (errno: 150 "Foreign key constraint is incorrectly formed")
+#
+# MDEV-23675 Assertion `pos < table->n_def' in dict_table_get_nth_col
+#
+CREATE TABLE t1 (pk int PRIMARY KEY, a INT, b INT, c INT, KEY(c),
+FOREIGN KEY fx (b) REFERENCES t1 (c))
+ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1,0,10,10);
+ALTER TABLE t1 DROP a, ALGORITHM=INSTANT;
+SET FOREIGN_KEY_CHECKS= 0;
+DROP INDEX fx ON t1;
+INSERT INTO t1 VALUES (2,11,11);
+DROP TABLE t1;
+SET FOREIGN_KEY_CHECKS=DEFAULT;
 # End of 10.4 tests
diff --git a/mysql-test/suite/innodb/t/foreign_key.test b/mysql-test/suite/innodb/t/foreign_key.test
index 9207fce6525..dab0736f712 100644
--- a/mysql-test/suite/innodb/t/foreign_key.test
+++ b/mysql-test/suite/innodb/t/foreign_key.test
@@ -741,6 +741,20 @@ DROP TABLE t1;
 CREATE TABLE t1 (a GEOMETRY, INDEX(a(8)),
 		 FOREIGN KEY (a) REFERENCES x (xx)) ENGINE=InnoDB;
 
+--echo #
+--echo # MDEV-23675 Assertion `pos < table->n_def' in dict_table_get_nth_col
+--echo #
+CREATE TABLE t1 (pk int PRIMARY KEY, a INT, b INT, c INT, KEY(c),
+FOREIGN KEY fx (b) REFERENCES t1 (c))
+ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1,0,10,10);
+ALTER TABLE t1 DROP a, ALGORITHM=INSTANT;
+SET FOREIGN_KEY_CHECKS= 0;
+DROP INDEX fx ON t1;
+INSERT INTO t1 VALUES (2,11,11);
+DROP TABLE t1;
+SET FOREIGN_KEY_CHECKS=DEFAULT;
+
 -- echo # End of 10.4 tests
 
 --source include/wait_until_count_sessions.inc
diff --git a/storage/innobase/row/row0ins.cc b/storage/innobase/row/row0ins.cc
index 9c913b0c9f2..a28489062b0 100644
--- a/storage/innobase/row/row0ins.cc
+++ b/storage/innobase/row/row0ins.cc
@@ -1908,8 +1908,14 @@ bool row_ins_foreign_index_entry(dict_foreign_t *foreign,
   {
     for (ulint j= 0; j < index->n_fields; j++)
     {
-      const char *col_name= dict_table_get_col_name(
-        index->table, dict_index_get_nth_col_no(index, j));
+      const dict_col_t *col= dict_index_get_nth_col(index, j);
+
+      /* A clustered index may contain instantly dropped columns,
+      which must be skipped. */
+      if (col->is_dropped())
+        continue;
+
+      const char *col_name= dict_table_get_col_name(index->table, col->ind);
       if (0 == innobase_strcasecmp(col_name, foreign->foreign_col_names[i]))
       {
         dfield_copy(&ref_entry->fields[i], &entry->fields[j]);