MDEV-16288 ALTER TABLE…ALGORITHM=DEFAULT does not override alter_algorithm

- Added the test case to prove that alter_algorithm variable doesn't
affect when ALTER statement during PREPARE PHASE or CREATE PROCEDURE.
Only when execution/call happens, alter uses the alter_algorithm
variable when user does not mention algorithm explicitly

mysql-test/suite/innodb/r/alter_algorithm2.result

+CREATE TABLE t1 (a INT)ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1);
+SET alter_algorithm='INPLACE';
+affected rows: 0
+PREPARE stmt FROM 'ALTER TABLE t1 ADD KEY idx(a)';
+affected rows: 0
+info: Statement prepared
+PREPARE stmt1 FROM 'ALTER TABLE t1 DROP KEY idx';
+affected rows: 0
+info: Statement prepared
+CREATE OR REPLACE PROCEDURE p1()
+BEGIN
+ALTER TABLE t1 ADD KEY idx2(a);
+END|
+affected rows: 0
+CREATE OR REPLACE PROCEDURE p2()
+BEGIN
+ALTER TABLE t1 DROP KEY idx2;
+END|
+affected rows: 0
+SET alter_algorithm='COPY';
+affected rows: 0
+EXECUTE stmt;
+affected rows: 1
+info: Records: 1  Duplicates: 0  Warnings: 0
+EXECUTE stmt1;
+affected rows: 1
+info: Records: 1  Duplicates: 0  Warnings: 0
+call p1();
+affected rows: 1
+call p2();
+affected rows: 1
+SET alter_algorithm='NOCOPY';
+affected rows: 0
+EXECUTE stmt;
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 0
+EXECUTE stmt1;
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 0
+call p1();
+affected rows: 0
+call p2();
+affected rows: 0
+SET alter_algorithm='INSTANT';
+affected rows: 0
+EXECUTE stmt;
+ERROR 0A000: ALGORITHM=INSTANT is not supported. Reason: ADD INDEX. Try ALGORITHM=NOCOPY
+call p1();
+ERROR 0A000: ALGORITHM=INSTANT is not supported. Reason: ADD INDEX. Try ALGORITHM=NOCOPY
+DROP TABLE t1;
+affected rows: 0
+DROP PROCEDURE p1;
+affected rows: 0
+DROP PROCEDURE p2;
+affected rows: 0

mysql-test/suite/innodb/t/alter_algorithm2.test

+--source include/have_innodb.inc
+CREATE TABLE t1 (a INT)ENGINE=InnoDB;
+INSERT INTO t1 VALUES(1);
+
+# alter_algorithm variable doesn't affect when ALTER stmt
+# during PREPARE PHASE or CREATE PROCEDURE
+# Only when execution/call happens, alter uses the alter_algorithm
+# variable when user does not mention algorithm explicitly.
+
+--enable_info
+SET alter_algorithm='INPLACE';
+PREPARE stmt FROM 'ALTER TABLE t1 ADD KEY idx(a)';
+PREPARE stmt1 FROM 'ALTER TABLE t1 DROP KEY idx';
+DELIMITER |;
+CREATE OR REPLACE PROCEDURE p1()
+BEGIN
+  ALTER TABLE t1 ADD KEY idx2(a);
+END|
+
+CREATE OR REPLACE PROCEDURE p2()
+BEGIN
+  ALTER TABLE t1 DROP KEY idx2;
+END|
+DELIMITER ;|
+
+SET alter_algorithm='COPY';
+EXECUTE stmt;
+EXECUTE stmt1;
+call p1();
+call p2();
+
+SET alter_algorithm='NOCOPY';
+EXECUTE stmt;
+EXECUTE stmt1;
+call p1();
+call p2();
+
+SET alter_algorithm='INSTANT';
+--error ER_ALTER_OPERATION_NOT_SUPPORTED_REASON
+EXECUTE stmt;
+--error ER_ALTER_OPERATION_NOT_SUPPORTED_REASON
+call p1();
+
+DROP TABLE t1;
+DROP PROCEDURE p1;
+DROP PROCEDURE p2;
+--disable_info