MDEV-29001 DROP DEFAULT makes SHOW CREATE non-idempotent

DROP DEFAULT adds DEFAULT NULL in case of nullable column. In case of
NOT NULL column it drops default expression if any exists.

Author: midenok

mysql-test/main/alter_table.result

@@ -3131,6 +3131,42 @@ alter table t1 drop constraint t1_fk_t2_id, drop t2_id, drop t2_id;
 ERROR 42000: Can't DROP COLUMN `t2_id`; check that it exists
 drop table t1, t2;
 #
+# MDEV-29001 DROP DEFAULT makes SHOW CREATE non-idempotent
+#
+SET @save_sql_mode=@@sql_mode;
+SET sql_mode=strict_all_tables;
+create table t1 (
+a int,
+b int default 0,
+c int not null,
+d int not null default 1);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT 0,
+  `c` int(11) NOT NULL,
+  `d` int(11) NOT NULL DEFAULT 1
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t1
+alter a drop default,
+alter b drop default,
+alter c drop default,
+alter d drop default;
+SHOW create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  `c` int(11) NOT NULL,
+  `d` int(11) NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+insert t1 values (default, default, default, default);
+ERROR HY000: Field 'c' doesn't have a default value
+insert t1 values (default, default, 0, 0);
+drop table t1;
+set sql_mode= @save_sql_mode;
+#
 # End of 10.6 tests
 #
 #

mysql-test/main/alter_table.test

@@ -2417,6 +2417,30 @@ create table t1(id int primary key, t2_id int, constraint t1_fk_t2_id foreign ke
 alter table t1 drop constraint t1_fk_t2_id, drop t2_id, drop t2_id;
 drop table t1, t2;
 
+--echo #
+--echo # MDEV-29001 DROP DEFAULT makes SHOW CREATE non-idempotent
+--echo #
+SET @save_sql_mode=@@sql_mode;
+SET sql_mode=strict_all_tables;
+create table t1 (
+  a int,
+  b int default 0,
+  c int not null,
+  d int not null default 1);
+show create table t1;
+alter table t1
+  alter a drop default,
+  alter b drop default,
+  alter c drop default,
+  alter d drop default;
+SHOW create table t1;
+--error ER_NO_DEFAULT_FOR_FIELD
+insert t1 values (default, default, default, default);
+insert t1 values (default, default, 0, 0);
+
+drop table t1;
+set sql_mode= @save_sql_mode;
+
 --echo #
 --echo # End of 10.6 tests
 --echo #

mysql-test/main/column_compression_parts.result

@@ -127,7 +127,6 @@ ALTER TABLE t1 MODIFY COLUMN a VARCHAR(1000);
 ALTER TABLE t1 ALTER COLUMN a DROP DEFAULT;
 INSERT INTO t1 VALUES (REPEAT('b',100),11);
 INSERT INTO t1 VALUES (default,10);
-ERROR HY000: Field 'a' doesn't have a default value
 ALTER TABLE t1 MODIFY COLUMN a VARCHAR(1000) COMPRESSED;
 SHOW CREATE TABLE t1;
 Table	Create Table
@@ -139,6 +138,7 @@ t1	CREATE TABLE `t1` (
 (PARTITION `p0` VALUES LESS THAN (100,'sss') ENGINE = MyISAM)
 SELECT * from t1 ORDER BY id;
 a	id
+NULL	10
 bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb	11
 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa	23
 zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz	24

mysql-test/main/column_compression_parts.test

@@ -72,7 +72,6 @@ ALTER TABLE t1 ALTER COLUMN a DROP DEFAULT;
 ALTER TABLE t1 MODIFY COLUMN a VARCHAR(1000);
 ALTER TABLE t1 ALTER COLUMN a DROP DEFAULT;
 INSERT INTO t1 VALUES (REPEAT('b',100),11);
---error ER_NO_DEFAULT_FOR_FIELD
 INSERT INTO t1 VALUES (default,10);
 
 ALTER TABLE t1 MODIFY COLUMN a VARCHAR(1000) COMPRESSED;