This is a valid SQL statement...
SELECT Host FROM Host WHERE (
Index = 1)
The above returns 1 record. Column is named 'Host' and table is named 'Host', and the table has a primary key on column 'Index'. I happen to be using MariaDB for the SQL back end.
However, the following returns zero results via the node-red-contrib-mysql node...
msg.topic = "SELECT Host FROM Host WHERE (`Index` = 1)";
Color me surprised!