MDEV-22230 : Unexpected ER_ERROR_ON_RENAME upon DROP non-existing FOREIGN KEY

mysql_prepare_alter_table(): Alter table should check whether
foreign key exists when it expected to exists and
report the error in early stage

dict_foreign_parse_drop_constraints(): Don't throw error if the
foreign key constraints doesn't exist when if exists is given
in the statement.

mysql-test/main/alter_table.result

@@ -1998,8 +1998,7 @@ ALTER TABLE ti1 DROP FOREIGN KEY fi1;
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
 ALTER TABLE tm1 DROP FOREIGN KEY fm1;
-affected rows: 2
+ERROR 42000: Can't DROP FOREIGN KEY `fm1`; check that it exists
-info: Records: 2  Duplicates: 0  Warnings: 0
 ALTER TABLE ti1 RENAME TO ti3;
 affected rows: 0
 ALTER TABLE tm1 RENAME TO tm3;

mysql-test/main/alter_table.test

@@ -1700,6 +1700,7 @@ ALTER TABLE ti1 DROP PRIMARY KEY;
 ALTER TABLE tm1 DROP PRIMARY KEY;
 
 ALTER TABLE ti1 DROP FOREIGN KEY fi1;
+--error ER_CANT_DROP_FIELD_OR_KEY
 ALTER TABLE tm1 DROP FOREIGN KEY fm1;
 
 ALTER TABLE ti1 RENAME TO ti3;

mysql-test/main/type_ranges.result

@@ -144,8 +144,10 @@ alter short drop default,
 DROP INDEX utiny,
 DROP INDEX ushort,
 DROP PRIMARY KEY,
-DROP FOREIGN KEY any_name,
+DROP FOREIGN KEY IF EXISTS any_name,
 ADD INDEX (auto);
+Warnings:
+Note	1091	Can't DROP FOREIGN KEY `any_name`; check that it exists
 LOCK TABLES t1 WRITE;
 ALTER TABLE t1 
 RENAME as t2,

mysql-test/main/type_ranges.test

@@ -76,7 +76,7 @@ alter short drop default,
 DROP INDEX utiny,
 DROP INDEX ushort,
 DROP PRIMARY KEY,
-DROP FOREIGN KEY any_name,
+DROP FOREIGN KEY IF EXISTS any_name,
 ADD INDEX (auto);
 
 LOCK TABLES t1 WRITE;

mysql-test/suite/innodb/r/fk_drop_alter.result

@@ -0,0 +1,44 @@
+#
+#  MDEV-22230 : Unexpected ER_ERROR_ON_RENAME upon DROP
+#	non-existing FOREIGN KEY
+#
+CREATE TABLE t1 (a INT) ENGINE=InnoDB;
+ALTER TABLE t1 DROP FOREIGN KEY x, ALGORITHM=COPY;
+ERROR 42000: Can't DROP FOREIGN KEY `x`; check that it exists
+ALTER TABLE t1 DROP FOREIGN KEY x, ALGORITHM=INPLACE;
+ERROR 42000: Can't DROP FOREIGN KEY `x`; check that it exists
+DROP TABLE t1;
+CREATE TABLE t1 (a INT, KEY(a)) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT, FOREIGN KEY fk_id (a) REFERENCES t1(a))ENGINE=InnoDB;
+CREATE TABLE t3 (a INT, FOREIGN KEY fk_1 (a) REFERENCES t1(a))ENGINE=InnoDB;
+ALTER TABLE t3 DROP FOREIGN KEY IF EXISTS fk_id;
+Warnings:
+Note	1091	Can't DROP FOREIGN KEY `fk_id`; check that it exists
+DROP TABLE t3, t2;
+ALTER TABLE t1 MODIFY COLUMN a VARCHAR(2), DROP FOREIGN KEY IF EXISTS x;
+Warnings:
+Note	1091	Can't DROP FOREIGN KEY `x`; check that it exists
+DROP TABLE t1;
+CREATE DATABASE best;
+CREATE TABLE best.t1(f1 INT, KEY(f1))ENGINE=InnoDB;
+CREATE TABLE best.t2(f1 INT, FOREIGN KEY foo(f1) REFERENCES t1(f1))ENGINE=InnoDB;
+CREATE TABLE t1(f1 INT, KEY(f1))ENGINE=InnoDB;
+CREATE TABLE t2(f1 INT, FOREIGN KEY foo(f1) REFERENCES t1(f1))ENGINE=InnoDB;
+ALTER TABLE t2 DROP FOREIGN KEY foo;
+ALTER TABLE t2 DROP FOREIGN KEY foo;
+ERROR 42000: Can't DROP FOREIGN KEY `foo`; check that it exists
+ALTER TABLE t2 DROP FOREIGN KEY IF EXISTS foo;
+Warnings:
+Note	1091	Can't DROP FOREIGN KEY `foo`; check that it exists
+SHOW CREATE TABLE best.t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `f1` int(11) DEFAULT NULL,
+  KEY `foo` (`f1`),
+  CONSTRAINT `foo` FOREIGN KEY (`f1`) REFERENCES `t1` (`f1`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN;
+ID	FOR_NAME	REF_NAME	N_COLS	TYPE
+best/foo	best/t2	best/t1	1	0
+DROP TABLE best.t2, best.t1, t2, t1;
+DROP DATABASE best;

mysql-test/suite/innodb/t/fk_drop_alter.test

@@ -0,0 +1,35 @@
+--source include/have_innodb.inc
+--echo #
+--echo #  MDEV-22230 : Unexpected ER_ERROR_ON_RENAME upon DROP
+--echo #	non-existing FOREIGN KEY
+--echo #
+CREATE TABLE t1 (a INT) ENGINE=InnoDB;
+--error ER_CANT_DROP_FIELD_OR_KEY
+ALTER TABLE t1 DROP FOREIGN KEY x, ALGORITHM=COPY;
+--error ER_CANT_DROP_FIELD_OR_KEY
+ALTER TABLE t1 DROP FOREIGN KEY x, ALGORITHM=INPLACE;
+# Cleanup
+DROP TABLE t1;
+
+CREATE TABLE t1 (a INT, KEY(a)) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT, FOREIGN KEY fk_id (a) REFERENCES t1(a))ENGINE=InnoDB;
+CREATE TABLE t3 (a INT, FOREIGN KEY fk_1 (a) REFERENCES t1(a))ENGINE=InnoDB;
+ALTER TABLE t3 DROP FOREIGN KEY IF EXISTS fk_id;
+DROP TABLE t3, t2;
+ALTER TABLE t1 MODIFY COLUMN a VARCHAR(2), DROP FOREIGN KEY IF EXISTS x;
+DROP TABLE t1;
+
+CREATE DATABASE best;
+CREATE TABLE best.t1(f1 INT, KEY(f1))ENGINE=InnoDB;
+CREATE TABLE best.t2(f1 INT, FOREIGN KEY foo(f1) REFERENCES t1(f1))ENGINE=InnoDB;
+
+CREATE TABLE t1(f1 INT, KEY(f1))ENGINE=InnoDB;
+CREATE TABLE t2(f1 INT, FOREIGN KEY foo(f1) REFERENCES t1(f1))ENGINE=InnoDB;
+ALTER TABLE t2 DROP FOREIGN KEY foo;
+--error ER_CANT_DROP_FIELD_OR_KEY
+ALTER TABLE t2 DROP FOREIGN KEY foo;
+ALTER TABLE t2 DROP FOREIGN KEY IF EXISTS foo;
+SHOW CREATE TABLE best.t2;
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN;
+DROP TABLE best.t2, best.t1, t2, t1;
+DROP DATABASE best;

sql/sql_table.cc

@@ -9056,6 +9056,30 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
         goto err;
       case Alter_drop::FOREIGN_KEY:
         // Leave the DROP FOREIGN KEY names in the alter_info->drop_list.
+        /* If this is DROP FOREIGN KEY without IF EXIST,
+        we can now check does it exists and if not report a error. */
+        if (!drop->drop_if_exists)
+        {
+          List <FOREIGN_KEY_INFO> fk_child_key_list;
+          table->file->get_foreign_key_list(thd, &fk_child_key_list);
+          if (fk_child_key_list.is_empty())
+          {
+	fk_not_found:
+            my_error(ER_CANT_DROP_FIELD_OR_KEY, MYF(0), drop->type_name(),
+                     drop->name);
+            goto err;
+          }
+          List_iterator<FOREIGN_KEY_INFO> fk_key_it(fk_child_key_list);
+          while (FOREIGN_KEY_INFO *f_key= fk_key_it++)
+          {
+            if (my_strcasecmp(system_charset_info, f_key->foreign_id->str,
+                              drop->name) == 0)
+              goto fk_found;
+          }
+          goto fk_not_found;
+        fk_found:
+          break;
+        }
         break;
       }
     }

storage/innobase/dict/dict0dict.cc

@@ -4592,6 +4592,7 @@ dict_foreign_parse_drop_constraints(
 	const char*		ptr1;
 	const char*		id;
 	CHARSET_INFO*		cs;
+	bool			if_exists = false;
 
 	ut_a(trx->mysql_thd);
 
@@ -4645,6 +4646,7 @@ loop:
 		ptr1 = dict_accept(cs, ptr1, "EXISTS", &success);
 		if (success) {
 			ptr = ptr1;
+			if_exists = true;
 		}
 	}
 
@@ -4655,14 +4657,14 @@ loop:
 		goto syntax_error;
 	}
 
-	ut_a(*n < 1000);
-	(*constraints_to_drop)[*n] = id;
-	(*n)++;
-
 	if (std::find_if(table->foreign_set.begin(),
-			 table->foreign_set.end(),
+			    table->foreign_set.end(),
-			 dict_foreign_matches_id(id))
+			    dict_foreign_matches_id(id))
-	    == table->foreign_set.end()) {
+	        == table->foreign_set.end()) {
+
+		if (if_exists) {
+			goto loop;
+		}
 
 		if (!srv_read_only_mode) {
 			FILE*	ef = dict_foreign_err_file;
@@ -4684,6 +4686,9 @@ loop:
 		return(DB_CANNOT_DROP_CONSTRAINT);
 	}
 
+	ut_a(*n < 1000);
+	(*constraints_to_drop)[*n] = id;
+	(*n)++;
 	goto loop;
 
 syntax_error: