MDEV-8960: Can't refer the same column twice in one ALTER TABLE

Problem was that if column was created in alter table when
it was refered again it was not tried to find from list
of current columns.

mysql_prepare_alter_table:
  There is two cases
    (1) If alter table adds a new column and then later alter
        changes the field definition, there was no check from
	list of new columns, instead an incorrect error was given.
    (2) If alter table adds a new column and then later alter
        changes the default, there was no check from list of
	new columns, instead an incorrect error was given.

mysql-test/r/alter_table.result

@@ -2112,3 +2112,55 @@ t1	CREATE TABLE `t1` (
   `b` int(11) DEFAULT NULL
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8
 DROP TABLE t1;
+#
+# MDEV-8960 Can't refer the same column twice in one ALTER TABLE
+#
+CREATE TABLE t1 (
+`a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL,
+ALTER COLUMN `consultant_id` DROP DEFAULT;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `consultant_id` int(11) NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8
+DROP TABLE t1;
+CREATE TABLE t1 (
+`a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL,
+ALTER COLUMN `consultant_id` SET DEFAULT 2;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `consultant_id` int(11) NOT NULL DEFAULT '2'
+) ENGINE=MyISAM DEFAULT CHARSET=utf8
+DROP TABLE t1;
+CREATE TABLE t1 (
+`a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL DEFAULT 2,
+ALTER COLUMN `consultant_id` DROP DEFAULT;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `consultant_id` int(11) NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8
+DROP TABLE t1;
+CREATE TABLE t1 (
+`a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL DEFAULT 2,
+ALTER COLUMN `consultant_id` DROP DEFAULT,
+MODIFY COLUMN `consultant_id` BIGINT;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `consultant_id` bigint(20) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8
+DROP TABLE t1;

mysql-test/t/alter_table.test

@@ -1767,3 +1767,45 @@ SHOW CREATE TABLE t1;
 ALTER TABLE t1 CONVERT TO CHARACTER SET utf8;
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-8960 Can't refer the same column twice in one ALTER TABLE
+--echo #
+
+CREATE TABLE t1 (
+  `a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL,
+ALTER COLUMN `consultant_id` DROP DEFAULT;
+
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (
+  `a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL,
+ALTER COLUMN `consultant_id` SET DEFAULT 2;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (
+  `a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL DEFAULT 2,
+ALTER COLUMN `consultant_id` DROP DEFAULT;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (
+  `a` int(11) DEFAULT NULL
+) DEFAULT CHARSET=utf8;
+
+ALTER TABLE t1 ADD COLUMN `consultant_id` integer NOT NULL DEFAULT 2,
+ALTER COLUMN `consultant_id` DROP DEFAULT,
+MODIFY COLUMN `consultant_id` BIGINT;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

sql/sql_table.cc

@@ -7503,9 +7503,25 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
   {
     if (def->change && ! def->field)
     {
-      my_error(ER_BAD_FIELD_ERROR, MYF(0), def->change,
-               table->s->table_name.str);
-      goto err;
+      /*
+        Check if there is modify for newly added field.
+      */
+      Create_field *find;
+      find_it.rewind();
+      while((find=find_it++))
+      {
+        if (!my_strcasecmp(system_charset_info,find->field_name, def->field_name))
+          break;
+      }
+
+      if (find && !find->field)
+	find_it.remove();
+      else
+      {
+        my_error(ER_BAD_FIELD_ERROR, MYF(0), def->change,
+                 table->s->table_name.str);
+        goto err;
+      }
     }
     /*
       Check that the DATE/DATETIME not null field we are going to add is
@@ -7571,6 +7587,29 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
         find_it.after(def);			// Put column after this
       }
     }
+    /*
+      Check if there is alter for newly added field.
+    */
+    alter_it.rewind();
+    Alter_column *alter;
+    while ((alter=alter_it++))
+    {
+      if (!my_strcasecmp(system_charset_info,def->field_name, alter->name))
+        break;
+    }
+    if (alter)
+    {
+      if (def->sql_type == MYSQL_TYPE_BLOB)
+      {
+        my_error(ER_BLOB_CANT_HAVE_DEFAULT, MYF(0), def->change);
+        goto err;
+      }
+      if ((def->def=alter->def))              // Use new default
+        def->flags&= ~NO_DEFAULT_VALUE_FLAG;
+      else
+        def->flags|= NO_DEFAULT_VALUE_FLAG;
+      alter_it.remove();
+    }
   }
   if (alter_info->alter_list.elements)
   {