MDEV-25078: ALTER INDEX is inconsistent with ADD/DROP/RENAME index

Support IF EXISTS in the command that alter index visibility:

  ALTER TABLE ALTER (KEY|INDEX) [IF EXISTS] index_name [NOT] IGNORED

3 files changed, 33 insertions, 5 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 2df0651886f..2fa50882ebf 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -390,13 +390,14 @@ public:
 class Alter_index_ignorability: public Sql_alloc
 {
 public:
-  Alter_index_ignorability(const char *name, bool is_ignored) :
-    m_name(name), m_is_ignored(is_ignored)
+  Alter_index_ignorability(const char *name, bool is_ignored, bool if_exists) :
+    m_name(name), m_is_ignored(is_ignored), m_if_exists(if_exists)
   {
     assert(name != NULL);
   }
 
   const char *name() const { return m_name; }
+  bool if_exists() const { return m_if_exists; }
 
   /* The ignorability after the operation is performed. */
   bool is_ignored() const { return m_is_ignored; }
@@ -406,6 +407,7 @@ public:
 private:
   const char *m_name;
   bool m_is_ignored;
+  bool m_if_exists;
 };
 
 
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 6be126655fc..cd48f58da10 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -5829,7 +5829,33 @@ drop_create_field:
       rename_key_it.remove();
     }
   }
-
+  /* Handle ALTER KEY IF EXISTS. */
+  {
+    List_iterator<Alter_index_ignorability> ignor_it(alter_info->alter_index_ignorability_list);
+    Alter_index_ignorability *aii;
+    while ((aii= ignor_it++))
+    {
+      if (!aii->if_exists())
+        continue;
+      bool exists= false;
+      for (uint n_key= 0; n_key < table->s->keys; n_key++)
+      {
+        if (my_strcasecmp(system_charset_info, aii->name(),
+                          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),
+                          aii->name(), table->s->table_name.str);
+      ignor_it.remove();
+    }
+  }
   /* ALTER TABLE ADD KEY IF NOT EXISTS */
   /* ALTER TABLE ADD FOREIGN KEY IF NOT EXISTS */
   {
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 931e5175f48..d1f22006e1d 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -7832,11 +7832,11 @@ alter_list_item:
             if (unlikely(Lex->add_alter_list($4, $7, $3)))
               MYSQL_YYABORT;
           }
-        | ALTER key_or_index ident ignorability
+        | ALTER key_or_index opt_if_exists_table_element ident ignorability
           {
             LEX *lex= Lex;
             Alter_index_ignorability *ac= new (thd->mem_root)
-                                        Alter_index_ignorability($3.str, $4);
+                                        Alter_index_ignorability($4.str, $5, $3);
             if (ac == NULL)
               MYSQL_YYABORT;
             lex->alter_info.alter_index_ignorability_list.push_back(ac);