MDEV-28152 wip wip wip alter sequence as <new_value_type>bb-11.0-mdev-28152-alter-value-type

Basic case:
- start with a narrow value type, the alter to a wider type without
  changing any other metadata

Advanced cases to fix once the basic case works:
- start with a wider value type, then alter to a narrower type with
  smaller metadata values in range for the narrower value type
- start with a narrower value type, then alter to a wider type with
  bigger metadata values out of range for the narrower type but in
  range for the wider type

4 files changed, 65 insertions, 5 deletions

diff --git a/mysql-test/suite/sql_sequence/alter.test b/mysql-test/suite/sql_sequence/alter.test
index a5e6245d609..8457a824723 100644
--- a/mysql-test/suite/sql_sequence/alter.test
+++ b/mysql-test/suite/sql_sequence/alter.test
@@ -161,3 +161,36 @@ CREATE SEQUENCE s;
 ALTER TABLE s ORDER BY cache_size;
 SELECT NEXTVAL(s);
 DROP SEQUENCE s;
+
+
+--echo #
+--echo # MDEV-28152 Features for sequence
+--echo #
+
+create or replace sequence t1 as bigint;
+show create sequence t1;
+show create table t1;
+alter sequence t1 as tinyint;
+show create sequence t1;
+show create table t1;
+
+create or replace sequence t1 as bigint maxvalue 123;
+show create sequence t1;
+show create table t1;
+alter sequence t1 as tinyint;
+show create sequence t1;
+show create table t1;
+
+create or replace sequence t1 as tinyint;
+show create sequence t1;
+show create table t1;
+alter sequence t1 as bigint;
+show create sequence t1;
+show create table t1;
+
+create or replace sequence t1 as int unsigned;
+show create sequence t1;
+show create table t1;
+alter sequence t1 as int;
+show create sequence t1;
+show create table t1;
diff --git a/sql/sql_sequence.cc b/sql/sql_sequence.cc
index 9ac7870852c..06d581164c9 100644
--- a/sql/sql_sequence.cc
+++ b/sql/sql_sequence.cc
@@ -353,7 +353,7 @@ err:
     true        Failure (out of memory)
 */
 
-bool sequence_definition::prepare_sequence_fields(List<Create_field> *fields)
+bool sequence_definition::prepare_sequence_fields(List<Create_field> *fields, bool alter)
 {
   DBUG_ENTER("prepare_sequence_fields");
   const Sequence_row_definition row_def= sequence_structure(value_type_handler());
@@ -374,6 +374,8 @@ bool sequence_definition::prepare_sequence_fields(List<Create_field> *fields)
     new_field->char_length= field_info->length;
     new_field->comment=     field_info->comment;
     new_field->flags=       field_info->flags;
+    if (alter)
+      new_field->change =   field_name;
     if (unlikely(fields->push_back(new_field)))
       DBUG_RETURN(TRUE); /* purify inspected */
   }
@@ -527,9 +529,9 @@ SEQUENCE::~SEQUENCE()
   A sequence table can have many readers (trough normal SELECT's).
 
   We mark that we have a write lock in the table object so that
-  ha_sequence::ha_write() can check if we have a lock. If already locked, then
+  ha_sequence::write_row() can check if we have a lock. If already locked, then
   ha_write() knows that we are running a sequence operation. If not, then
-  ha_write() knows that it's an INSERT.
+  ha_write() knows that it's an INSERT statement.
 */
 
 void SEQUENCE::write_lock(TABLE *table)
@@ -1029,6 +1031,7 @@ bool Sql_cmd_alter_sequence::execute(THD *thd)
 #endif /* WITH_WSREP */
   if (if_exists())
     thd->push_internal_handler(&no_such_table_handler);
+  first_table->mdl_request.set_type(MDL_SHARED_WRITE);
   error= open_and_lock_tables(thd, first_table, FALSE, 0);
   if (if_exists())
   {
@@ -1101,6 +1104,30 @@ bool Sql_cmd_alter_sequence::execute(THD *thd)
     goto end;
   }
 
+  if (new_seq->value_type_handler() != seq->value_type_handler())
+  {
+    // delete row?
+    // alter table
+  /* Set lock type which is appropriate for ALTER TABLE. */
+  // first_table->lock_type= TL_READ_NO_INSERT;
+  // /* Same applies to MDL request. */
+  // first_table->mdl_request.set_type(MDL_SHARED_NO_WRITE);
+    Alter_info alter_info;
+    alter_info.flags = ALTER_CHANGE_COLUMN;
+    // alter_info.requested_lock = Alter_info::ALTER_TABLE_LOCK_NONE;
+    if (new_seq->prepare_sequence_fields(&alter_info.create_list, true))
+    {
+      // fixme: emit error.
+      abort();
+    }
+    Table_specification_st create_info;
+    create_info.init();
+    create_info.alter_info= &alter_info;
+    bool res= mysql_alter_table(thd, &null_clex_str, &null_clex_str, &create_info, first_table, &alter_info, 0, (ORDER *) 0, 0, 0);
+    if (res)
+      DBUG_RETURN(0);        
+  }
+
   if (likely(!(error= new_seq->write(table, 1))))
   {
     /* Store the sequence values in table share */
diff --git a/sql/sql_sequence.h b/sql/sql_sequence.h
index 23e185d8271..0de92a90639 100644
--- a/sql/sql_sequence.h
+++ b/sql/sql_sequence.h
@@ -108,7 +108,7 @@ public:
                         max_value, cache, round));
   }
   static bool is_allowed_value_type(enum_field_types type);
-  bool prepare_sequence_fields(List<Create_field> *fields);
+  bool prepare_sequence_fields(List<Create_field> *fields, bool alter);
   
 protected:
   /*
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index de5c94979c9..a359478145c 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -2436,7 +2436,7 @@ create:
 
             /* No fields specified, generate them */
             if (unlikely(lex->create_info.seq_create_info->prepare_sequence_fields(
-                &lex->alter_info.create_list)))
+                                                                                   &lex->alter_info.create_list, false)))
                MYSQL_YYABORT;
 
             /* CREATE SEQUENCE always creates a sequence */