MDEV-16290 ALTER TABLE ... RENAME COLUMN syntax

The existing syntax for renaming a column uses "ALTER TABLE ...  CHANGE"
command. This requires full column specification to rename the column.
This patch adds new syntax "ALTER TABLE ...  RENAME COLUMN", which do not
expect users to provide full column specification.  It means that the new
syntax would pick in-place or copy algorithm in the same way as that of
existing "ALTER TABLE ... CHANGE" command. The existing syntax
"ALTER TABLE ... CHANGE" will continue to work.

Syntax changes
==============

ALTER TABLE tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

Following is a new <alter_specification> added:

 | RENAME COLUMN <oldname> TO <newname>

Where <oldname> and <newname> are identifiers for old name and new
name of the column.

Related to: WL#10761

5 files changed, 82 insertions, 34 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 13b2659789d..6a7c0cd4d94 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -333,17 +333,25 @@ public:
 
 class Alter_column :public Sql_alloc {
 public:
-  const char *name;
+  LEX_CSTRING name;
+  LEX_CSTRING new_name;
   Virtual_column_info *default_value;
   bool alter_if_exists;
-  Alter_column(const char *par_name, Virtual_column_info *expr, bool par_exists)
-    :name(par_name), default_value(expr), alter_if_exists(par_exists) {}
+  Alter_column(LEX_CSTRING par_name, Virtual_column_info *expr, bool par_exists)
+    :name(par_name), new_name{NULL, 0}, default_value(expr), alter_if_exists(par_exists) {}
+  Alter_column(LEX_CSTRING par_name, LEX_CSTRING _new_name)
+    :name(par_name), new_name(_new_name), default_value(NULL), alter_if_exists(false) {}
   /**
     Used to make a clone of this object for ALTER/CREATE TABLE
     @sa comment for Key_part_spec::clone
   */
   Alter_column *clone(MEM_ROOT *mem_root) const
     { return new (mem_root) Alter_column(*this); }
+  bool is_rename()
+  {
+    DBUG_ASSERT(!new_name.str || !default_value);
+    return new_name.str;
+  }
 };
 
 
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index ea60d0cebd0..3ab1a46f95d 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -511,7 +511,7 @@ void LEX::add_key_to_list(LEX_CSTRING *field_name,
 }
 
 
-bool LEX::add_alter_list(const char *name, Virtual_column_info *expr,
+bool LEX::add_alter_list(LEX_CSTRING name, Virtual_column_info *expr,
                          bool exists)
 {
   MEM_ROOT *mem_root= thd->mem_root;
@@ -524,6 +524,17 @@ bool LEX::add_alter_list(const char *name, Virtual_column_info *expr,
 }
 
 
+bool LEX::add_alter_list(LEX_CSTRING name, LEX_CSTRING new_name)
+{
+  Alter_column *ac= new (thd->mem_root) Alter_column(name, new_name);
+  if (unlikely(ac == NULL))
+    return true;
+  alter_info.alter_list.push_back(ac, thd->mem_root);
+  alter_info.flags|= ALTER_RENAME_COLUMN;
+  return false;
+}
+
+
 void LEX::init_last_field(Column_definition *field,
                           const LEX_CSTRING *field_name,
                           const CHARSET_INFO *cs)
diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 2d08aa6c79b..c75833ae282 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -4320,8 +4320,9 @@ public:
     alter_info.check_constraint_list.push_back(constr);
     return false;
   }
-  bool add_alter_list(const char *par_name, Virtual_column_info *expr,
+  bool add_alter_list(LEX_CSTRING par_name, Virtual_column_info *expr,
                       bool par_exists);
+  bool add_alter_list(LEX_CSTRING name, LEX_CSTRING new_name);
   void set_command(enum_sql_command command,
                    DDL_options_st options)
   {
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 240f001f7de..b5cc07b1411 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -6167,7 +6167,7 @@ drop_create_field:
       for (f_ptr=table->field; *f_ptr; f_ptr++)
       {
         if (my_strcasecmp(system_charset_info,
-                           acol->name, (*f_ptr)->field_name.str) == 0)
+                           acol->name.str, (*f_ptr)->field_name.str) == 0)
           break;
       }
       if (unlikely(*f_ptr == NULL))
@@ -6175,7 +6175,7 @@ drop_create_field:
         push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
                             ER_BAD_FIELD_ERROR,
                             ER_THD(thd, ER_BAD_FIELD_ERROR),
-                            acol->name, table->s->table_name.str);
+                            acol->name.str, table->s->table_name.str);
         it.remove();
         if (alter_info->alter_list.is_empty())
         {
@@ -8138,24 +8138,6 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       continue;
     }
 
-    /*
-      If we are doing a rename of a column, update all references in virtual
-      column expressions, constraints and defaults to use the new column name
-    */
-    if (alter_info->flags & ALTER_RENAME_COLUMN)
-    {
-      if (field->vcol_info)
-        field->vcol_info->expr->walk(&Item::rename_fields_processor, 1,
-                                     &column_rename_param);
-      if (field->check_constraint)
-        field->check_constraint->expr->walk(&Item::rename_fields_processor, 1,
-                                            &column_rename_param);
-      if (field->default_value)
-        field->default_value->expr->walk(&Item::rename_fields_processor, 1,
-                                         &column_rename_param);
-      table->m_needs_reopen= 1; // because new column name is on thd->mem_root
-    }
-
     /* Check if field is changed */
     def_it.rewind();
     while ((def=def_it++))
@@ -8229,19 +8211,61 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       while ((alter=alter_it++))
       {
 	if (!my_strcasecmp(system_charset_info,field->field_name.str,
-                           alter->name))
+                           alter->name.str))
 	  break;
       }
       if (alter)
       {
-	if ((def->default_value= alter->default_value))
-          def->flags&= ~NO_DEFAULT_VALUE_FLAG;
+        if (alter->is_rename())
+        {
+          def->change= alter->name;
+          def->field_name= alter->new_name;
+          column_rename_param.fields.push_back(def);
+        }
         else
-          def->flags|= NO_DEFAULT_VALUE_FLAG;
+        {
+          if ((def->default_value= alter->default_value))
+            def->flags&= ~NO_DEFAULT_VALUE_FLAG;
+          else
+            def->flags|= NO_DEFAULT_VALUE_FLAG;
+        }
 	alter_it.remove();
       }
     }
   }
+
+  /*
+    If we are doing a rename of a column, update all references in virtual
+    column expressions, constraints and defaults to use the new column name
+  */
+  if (alter_info->flags & ALTER_RENAME_COLUMN)
+  {
+    alter_it.rewind();
+    Alter_column *alter;
+    while ((alter=alter_it++))
+    {
+      if (alter->is_rename())
+      {
+        my_error(ER_BAD_FIELD_ERROR, MYF(0), alter->name.str,
+                 table->s->table_name.str);
+        goto err;
+      }
+    }
+    for (f_ptr=table->field ; (field= *f_ptr) ; f_ptr++)
+    {
+      if (field->vcol_info)
+        field->vcol_info->expr->walk(&Item::rename_fields_processor, 1,
+                                    &column_rename_param);
+      if (field->check_constraint)
+        field->check_constraint->expr->walk(&Item::rename_fields_processor, 1,
+                                            &column_rename_param);
+      if (field->default_value)
+        field->default_value->expr->walk(&Item::rename_fields_processor, 1,
+                                        &column_rename_param);
+    }
+    table->m_needs_reopen= 1; // because new column name is on thd->mem_root
+  }
+
   dropped_sys_vers_fields &= VERS_SYSTEM_FIELD;
   if ((dropped_sys_vers_fields ||
        alter_info->flags & ALTER_DROP_PERIOD) &&
@@ -8357,7 +8381,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
     while ((alter=alter_it++))
     {
       if (!my_strcasecmp(system_charset_info,def->field_name.str,
-                         alter->name))
+                         alter->name.str))
         break;
     }
     if (alter)
@@ -8372,7 +8396,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
   if (unlikely(alter_info->alter_list.elements))
   {
     my_error(ER_BAD_FIELD_ERROR, MYF(0),
-             alter_info->alter_list.head()->name, table->s->table_name.str);
+             alter_info->alter_list.head()->name.str, table->s->table_name.str);
     goto err;
   }
   if (unlikely(!new_create_list.elements))
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index f24da3ed412..1d4a8a7e228 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -7705,13 +7705,12 @@ alter_list_item:
           }
         | ALTER opt_column opt_if_exists_table_element field_ident SET DEFAULT column_default_expr
           {
-            if (unlikely(Lex->add_alter_list($4.str, $7, $3)))
+            if (unlikely(Lex->add_alter_list($4, $7, $3)))
               MYSQL_YYABORT;
           }
         | ALTER opt_column opt_if_exists_table_element field_ident DROP DEFAULT
           {
-            if (unlikely(Lex->add_alter_list($4.str, (Virtual_column_info*) 0,
-                                             $3)))
+            if (unlikely(Lex->add_alter_list($4, (Virtual_column_info*) 0, $3)))
               MYSQL_YYABORT;
           }
         | RENAME opt_to table_ident
@@ -7728,6 +7727,11 @@ alter_list_item:
             lex->name= $3->table;
             lex->alter_info.flags|= ALTER_RENAME;
           }
+        | RENAME COLUMN_SYM ident TO_SYM ident
+          {
+            if (unlikely(Lex->add_alter_list($3, $5)))
+              MYSQL_YYABORT;
+          }
         | CONVERT_SYM TO_SYM charset charset_name_or_default opt_collate
           {
             if (!$4)