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

mysql-test/main/ignored_index.result

@@ -479,3 +479,52 @@ t1	CREATE TABLE `t1` (
   KEY `a` (`a`) IGNORED
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1;
+#
+#  MDEV-25078, part #2: allow IF EXISTS
+#
+create table t1 (a int, b int, c int, key(a), key(b), key(c));
+alter table t1 alter key if exists no_such_key ignored;
+Warnings:
+Note	1176	Key 'no_such_key' doesn't exist in table 't1'
+alter table t1 alter key if exists a ignored;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  `c` int(11) DEFAULT NULL,
+  KEY `a` (`a`) IGNORED,
+  KEY `b` (`b`),
+  KEY `c` (`c`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+alter table t1
+alter key if exists no_such_key ignored,
+alter key if exists c ignored ;
+Warnings:
+Note	1176	Key 'no_such_key' doesn't exist in table 't1'
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  `c` int(11) DEFAULT NULL,
+  KEY `a` (`a`) IGNORED,
+  KEY `b` (`b`),
+  KEY `c` (`c`) IGNORED
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+alter table t1 
+alter key if exists no_such_key not ignored, 
+alter key if exists c not ignored ;
+Warnings:
+Note	1176	Key 'no_such_key' doesn't exist in table 't1'
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  `c` int(11) DEFAULT NULL,
+  KEY `a` (`a`) IGNORED,
+  KEY `b` (`b`),
+  KEY `c` (`c`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;

mysql-test/main/ignored_index.test

@@ -442,3 +442,23 @@ CREATE TABLE t1 (a INT, KEY (a));
 ALTER TABLE t1 ALTER KEY a IGNORED;
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
+
+--echo #
+--echo #  MDEV-25078, part #2: allow IF EXISTS
+--echo #
+
+create table t1 (a int, b int, c int, key(a), key(b), key(c));
+alter table t1 alter key if exists no_such_key ignored;
+alter table t1 alter key if exists a ignored;
+show create table t1;
+alter table t1
+  alter key if exists no_such_key ignored,
+  alter key if exists c ignored ;
+show create table t1;
+alter table t1 
+  alter key if exists no_such_key not ignored, 
+  alter key if exists c not ignored ;
+show create table t1;
+drop table t1;
+
+

sql/sql_class.h

@@ -390,13 +390,14 @@ class Alter_rename_key : public Sql_alloc
 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 @@ class Alter_index_ignorability: public Sql_alloc
 private:
   const char *m_name;
   bool m_is_ignored;
+  bool m_if_exists;
 };
 
 

sql/sql_table.cc

@@ -5829,7 +5829,33 @@ handle_if_exists_options(THD *thd, TABLE *table, Alter_info *alter_info,
       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 */
   {

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);