MDEV-32795: ALTER SEQUENCE IF NOT EXISTS non_existing_seq Errors rather than note

Like all IF NOT EXISTS syntax, a Note should be generated.

The original commit of Seqeuences cleared the IF NOT EXISTS part
in the sql/sql_yacc.yy with lex->create_info.init(). Without this
bit set there was no way it could do anything other than error.

To remedy this removal, the sql_yacc.yy components have been
minimised as they where all set at the beginning of the ALTER.
This way the opt_if_not_exists correctly set the IF_EXISTS flag.

In MDEV-13005 (bb4dd70e) the error code changed, requiring
ER_UNKNOWN_SEQUENCES to be handled in the function
No_such_table_error_handler::handle_condition.

mysql-test/suite/sql_sequence/alter.result

@@ -210,8 +210,12 @@ create table t1 (a int);
 alter sequence t1 minvalue=100;
 ERROR 42S02: 'test.t1' is not a SEQUENCE
 drop table t1;
+#
+# MDEV-32795: ALTER SEQUENCE IF NOT EXISTS non_existing_seq Errors rather than note
+#
 alter sequence if exists t1 minvalue=100;
-ERROR 42S02: Unknown SEQUENCE: 't1'
+Warnings:
+Note	4091	Unknown SEQUENCE: 'test.t1'
 alter sequence t1 minvalue=100;
 ERROR 42S02: Unknown SEQUENCE: 't1'
 create sequence t1;

mysql-test/suite/sql_sequence/alter.test

@@ -120,8 +120,12 @@ create table t1 (a int);
 alter sequence t1 minvalue=100;
 drop table t1;
 
---error ER_UNKNOWN_SEQUENCES
+--echo #
+--echo # MDEV-32795: ALTER SEQUENCE IF NOT EXISTS non_existing_seq Errors rather than note
+--echo #
+
 alter sequence if exists t1 minvalue=100;
+
 --error ER_UNKNOWN_SEQUENCES
 alter sequence t1 minvalue=100;
 

sql/sql_base.cc

@@ -77,7 +77,9 @@ No_such_table_error_handler::handle_condition(THD *,
                                               Sql_condition ** cond_hdl)
 {
   *cond_hdl= NULL;
-  if (sql_errno == ER_NO_SUCH_TABLE || sql_errno == ER_NO_SUCH_TABLE_IN_ENGINE)
+  if (sql_errno == ER_NO_SUCH_TABLE
+      || sql_errno == ER_NO_SUCH_TABLE_IN_ENGINE
+      || sql_errno == ER_UNKNOWN_SEQUENCES)
   {
     m_handled_errors++;
     return TRUE;

sql/sql_yacc.yy

@@ -8128,11 +8128,7 @@ alter:
         | ALTER SEQUENCE_SYM opt_if_exists
           {
             LEX *lex= Lex;
-            lex->name= null_clex_str;
-            lex->table_type= TABLE_TYPE_UNKNOWN;
             lex->sql_command= SQLCOM_ALTER_SEQUENCE;
-            lex->create_info.init();
-            lex->no_write_to_binlog= 0;
             DBUG_ASSERT(!lex->m_sql_cmd);
             if (Lex->main_select_push())
               MYSQL_YYABORT;