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.

1 files changed, 42 insertions, 3 deletions

diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 2eff8fd5e2f..3ba3ec6847e 100644
--- a/sql/sql_table.cc
+++ b/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)
   {