VitessAware system variables of type boolean return NULL when the query is not passed to MySQL

[frouioui]

Overview of the Issue

When a query selects VitessAware system variables, without passing the query down to MySQL. A value of type NULL is returned.

This issue applies to boolean-typed variables.

Whenever the query implies being sent down to MySQL, the variable's value is correctly returned.

Reproduction Steps

Steps to reproduce this issue:

1. Set the value of the, for instance, autocommit variable:

mysql> set @@autocommit = 1;
Query OK, 0 rows affected (0.00 sec)

Can also be set with on.

2. Select the variable:

mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|         NULL |
+--------------+
1 row in set (0.01 sec)

3. Test the correct behavior, by selecting from a table:

mysql> select @@autocommit from corder;
+--------------+
| @@autocommit |
+--------------+
|            1 |
|            1 |
|            1 |
|            1 |
|            1 |
+--------------+
5 rows in set (0.00 sec)

Binary version

Version: 36110d81b (Git branch 'master') built on Fri Jan 15 16:45:21 CET 2021 by [email protected] using go1.15.5 darwin/amd64

Operating system and Environment details

Ran on the 101 local example.