MDEV-21889 IF EXISTS clause does not work for RENAME COLUMN and RENAME INDEX

mysql-test/main/alter_table.result

@@ -2594,6 +2594,11 @@ t1	CREATE TABLE `t1` (
   `c` float DEFAULT NULL
 ) ENGINE=DEFAULT_ENGINE DEFAULT CHARSET=latin1
 ALTER TABLE t1 RENAME COLUMN a TO m;
+ALTER TABLE t1 RENAME COLUMN a TO m;
+ERROR 42S22: Unknown column 'a' in 't1'
+ALTER TABLE t1 RENAME COLUMN IF EXISTS a TO m;
+Warnings:
+Note	1054	Unknown column 'a' in 't1'
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
@@ -2882,6 +2887,9 @@ t1	CREATE TABLE `t1` (
 #      exists, dropped or added within the same ALTER TABLE.
 alter table t1 rename key d to e;
 ERROR 42000: Key 'd' doesn't exist in table 't1'
+alter table t1 rename key if exists d to e;
+Warnings:
+Note	1176	Key 'd' doesn't exist in table 't1'
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (

mysql-test/main/alter_table.test

@@ -2110,6 +2110,9 @@ ALTER TABLE t1 RENAME COLUMN a TO a;
 --replace_result $default_engine DEFAULT_ENGINE " PAGE_CHECKSUM=1" ""
 SHOW CREATE TABLE t1;
 ALTER TABLE t1 RENAME COLUMN a TO m;
+--error ER_BAD_FIELD_ERROR
+ALTER TABLE t1 RENAME COLUMN a TO m;
+ALTER TABLE t1 RENAME COLUMN IF EXISTS a TO m;
 --replace_result $default_engine DEFAULT_ENGINE " PAGE_CHECKSUM=1" ""
 SHOW CREATE TABLE t1;
 SELECT * FROM t1;
@@ -2293,6 +2296,7 @@ show create table t1;
 --echo #      exists, dropped or added within the same ALTER TABLE.
 --error ER_KEY_DOES_NOT_EXISTS
 alter table t1 rename key d to e;
+alter table t1 rename key if exists d to e;
 show create table t1;
 --error ER_KEY_DOES_NOT_EXISTS
 alter table t1 drop key c, rename key c to d;

sql/sql_class.h

@@ -341,8 +341,8 @@ class Alter_column :public Sql_alloc {
   bool alter_if_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) {}
+  Alter_column(LEX_CSTRING par_name, LEX_CSTRING _new_name, bool exists)
+    :name(par_name), new_name(_new_name), default_value(NULL), alter_if_exists(exists) {}
   /**
     Used to make a clone of this object for ALTER/CREATE TABLE
     @sa comment for Key_part_spec::clone
@@ -362,9 +362,10 @@ class Alter_rename_key : public Sql_alloc
 public:
   LEX_CSTRING old_name;
   LEX_CSTRING new_name;
+  bool alter_if_exists;
 
-  Alter_rename_key(LEX_CSTRING old_name_arg, LEX_CSTRING new_name_arg)
-      : old_name(old_name_arg), new_name(new_name_arg) {}
+  Alter_rename_key(LEX_CSTRING old_name_arg, LEX_CSTRING new_name_arg, bool exists)
+      : old_name(old_name_arg), new_name(new_name_arg), alter_if_exists(exists) {}
 
   Alter_rename_key *clone(MEM_ROOT *mem_root) const
     { return new (mem_root) Alter_rename_key(*this); }

sql/sql_lex.cc

@@ -524,9 +524,9 @@ bool LEX::add_alter_list(LEX_CSTRING name, Virtual_column_info *expr,
 }
 
 
-bool LEX::add_alter_list(LEX_CSTRING name, LEX_CSTRING new_name)
+bool LEX::add_alter_list(LEX_CSTRING name, LEX_CSTRING new_name, bool exists)
 {
-  Alter_column *ac= new (thd->mem_root) Alter_column(name, new_name);
+  Alter_column *ac= new (thd->mem_root) Alter_column(name, new_name, exists);
   if (unlikely(ac == NULL))
     return true;
   alter_info.alter_list.push_back(ac, thd->mem_root);

sql/sql_lex.h

@@ -4323,7 +4323,7 @@ struct LEX: public Query_tables_list
   }
   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);
+  bool add_alter_list(LEX_CSTRING name, LEX_CSTRING new_name, bool exists);
   void set_command(enum_sql_command command,
                    DDL_options_st options)
   {

sql/sql_table.cc

@@ -6256,7 +6256,7 @@ handle_if_exists_options(THD *thd, TABLE *table, Alter_info *alter_info,
     }
   }
 
-  /* Handle ALTER COLUMN IF EXISTS SET/DROP DEFAULT. */
+  /* Handle ALTER/RENAME COLUMN IF EXISTS. */
   {
     List_iterator<Alter_column> it(alter_info->alter_list);
     Alter_column *acol;
@@ -6424,6 +6424,35 @@ handle_if_exists_options(THD *thd, TABLE *table, Alter_info *alter_info,
     alter_info->flags|= left_flags;
   }
 
+  /* Handle RENAME KEY IF EXISTS. */
+  {
+    List_iterator<Alter_rename_key> rename_key_it(alter_info->alter_rename_key_list);
+    Alter_rename_key *rename_key;
+    while ((rename_key= rename_key_it++))
+    {
+      if (!rename_key->alter_if_exists)
+        continue;
+      bool exists= false;
+      for (uint n_key= 0; n_key < table->s->keys; n_key++)
+      {
+        if (my_strcasecmp(system_charset_info,
+                          rename_key->old_name.str,
+                          table->key_info[n_key].name.str) == 0)
+        {
+          exists= true;
+          break;
+        }
+      }
+      if (exists)
+        continue;
+      push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                          ER_KEY_DOES_NOT_EXISTS,
+                          ER_THD(thd, ER_KEY_DOES_NOT_EXISTS),
+                          rename_key->old_name.str, table->s->table_name.str);
+      rename_key_it.remove();
+    }
+  }
+
   /* ALTER TABLE ADD KEY IF NOT EXISTS */
   /* ALTER TABLE ADD FOREIGN KEY IF NOT EXISTS */
   {

sql/sql_yacc.yy

@@ -7757,16 +7757,16 @@ alter_list_item:
             lex->name= $3->table;
             lex->alter_info.flags|= ALTER_RENAME;
           }
-        | RENAME COLUMN_SYM ident TO_SYM ident
+        | RENAME COLUMN_SYM opt_if_exists_table_element ident TO_SYM ident
           {
-            if (unlikely(Lex->add_alter_list($3, $5)))
+            if (unlikely(Lex->add_alter_list($4, $6, $3)))
               MYSQL_YYABORT;
           }
-        | RENAME key_or_index field_ident TO_SYM field_ident
+        | RENAME key_or_index opt_if_exists_table_element field_ident TO_SYM field_ident
           {
             LEX *lex=Lex;
             Alter_rename_key *ak= new (thd->mem_root)
-                                    Alter_rename_key($3, $5);
+                                    Alter_rename_key($4, $6, $3);
             if (ak == NULL)
               MYSQL_YYABORT;
             lex->alter_info.alter_rename_key_list.push_back(ak);