create
    definer = `mysql.sys`@localhost function sys.list_drop(in_list text, in_drop_value text) returns text comment '
Description
-----------

Takes a list, and a value to attempt to remove from the list, and returns the resulting list.

Useful for altering certain session variables, like sql_mode or optimizer_switch for instance.

Parameters
-----------

in_list (TEXT):
  The comma separated list to drop a value from

in_drop_value (TEXT):
  The value to drop from the input list

Returns
-----------

TEXT

Example
--------

mysql> select @@sql_mode;
+-----------------------------------------------------------------------------------------------+
| @@sql_mode                                                                                    |
+-----------------------------------------------------------------------------------------------+
| ANSI_QUOTES,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> set sql_mode = sys.list_drop(@@sql_mode, ''ONLY_FULL_GROUP_BY'');
Query OK, 0 rows affected (0.03 sec)

mysql> select @@sql_mode;
+----------------------------------------------------------------------------+
| @@sql_mode                                                                 |
+----------------------------------------------------------------------------+
| ANSI_QUOTES,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+----------------------------------------------------------------------------+
1 row in set (0.00 sec)

' deterministic sql security invoker
BEGIN
    IF (in_drop_value IS NULL) THEN
        SIGNAL SQLSTATE '02200'
           SET MESSAGE_TEXT = 'Function sys.list_drop: in_drop_value input variable should not be NULL',
               MYSQL_ERRNO = 1138;
    END IF;
    IF (in_list IS NULL OR LENGTH(in_list) = 0) THEN
        -- return the list as it was passed in
        RETURN in_list;
    END IF;
    -- ensure that leading / trailing commas are remove, support values with either spaces or not between commas
    RETURN (SELECT TRIM(BOTH ',' FROM REPLACE(REPLACE(CONCAT(',', in_list), CONCAT(',', in_drop_value), ''), CONCAT(', ', in_drop_value), '')));
END;

