Hi Oleg,

commit 8e6595cff0caa22d2bb81002505e52b5c52f5ab2 Author: Oleg Smirnov <olernov@gmail.com> Date: Tue Jan 11 20:25:11 2022 +0300

MDEV-10000 Add EXPLAIN FOR CONNECTION syntax support ...

diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy index 442644eddd6..74757970411 100644 --- a/sql/sql_yacc.yy +++ b/sql/sql_yacc.yy @@ -14121,6 +14122,15 @@ opt_describe_column: } ;

+explain_for_connection: + describe_command FOR_SYM CONNECTION_SYM expr + { + Lex->sql_command= SQLCOM_SHOW_EXPLAIN; + if (unlikely(prepare_schema_table(thd, Lex, 0, SCH_EXPLAIN))) + MYSQL_YYABORT; + add_value_to_list(thd, $4); + } + ;

This fails to intialize the statement properly. For SHOW EXPLAIN, the following is done at statement start: show: SHOW { LEX *lex=Lex; lex->wild=0; lex->ident= null_clex_str; if (Lex->main_select_push()) MYSQL_YYABORT; mysql_init_select(lex); lex->current_select->parsing_place= SELECT_LIST; lex->create_info.init(); } If you don't do it, EXPLAIN FOR CONNECTION may produce crashes (e.g. on my machine it was crash in JOIN::prepare due to select_lex->inner_sum_func_list=0xa5a5a5a5a5). The rest of the code looks ok. Let's have another review iteration once the aboveis fixed. I've also found one difference with MySQL, which I am not sure if we should fix: In MariaDB, if the target is not running something that has an query plan, SHOW EXPLAIN (and now EXPLAIN FOR CONNECTION) will produce this error: MariaDB [test]> show explain for 5; ERROR 1933 (HY000): Target is not running an EXPLAINable command while in MySQL it can be one of two: 1. Target is idle: mysql> explain for connection 8; Query OK, 0 rows affected (0.00 sec) 2. Target is running a command that's not supported: mysql> explain for connection 8; ERROR 3012 (HY000): EXPLAIN FOR CONNECTION command is supported only for SELECT/UPDATE/INSERT/DELETE/REPLACE I'm not sure we should try to imitate this behavior. BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net