SQL servers and MySQL, PostgreySQL, Oracle don't understand double quotes("). Thus your query should be free from double quotes(") and should only use single quotes(').
Back-trip(`) is optional to use in SQL and is used for table name, db name and column names.
If you are trying to write query in your back-end to call MySQL then you can use double quote(") or single quotes(') to assign query to a variable like:
let query = "select id, name from accounts";
//Or
let query = 'select id, name from accounts';
If ther's a where statement in your query and/or trying to insert a value and/or an update of value which is string use single quote(') for these values like:
let querySelect = "select id, name from accounts where name = 'John'";
let queryUpdate = "update accounts set name = 'John' where id = 8";
let queryInsert = "insert into accounts(name) values('John')";
//Please not that double quotes are only to be used in assigning string to our variable not in the query
//All these below will generate error
let querySelect = 'select id, name from accounts where name = "John"';
let queryUpdate = 'update accounts set name = "John" where id = 8';
let queryInsert = 'insert into accounts(name) values("John")';
//As MySQL or any SQL doesn't understand double quotes("), these all will generate error.
If you want to stay out of this confusion when to use double quotes(") and single quotes('), would recommend to stick with single quotes(') this will include backslash() like:
let query = 'select is, name from accounts where name = \'John\'';
Problem with double(") or single(') quotes arise when we had to assign some value dynamic and perform some string concatenation like:
let query = "select id, name from accounts where name = " + fName + " " + lName;
//This will generate error as it must be like name = 'John Smith' for SQL
//However our statement made it like name = John Smith
//In order to resolve such errors use
let query = "select id, name from accounts where name = '" + fName + " " + lName + "'";
//Or using backslash(\)
let query = 'select id, name from accounts where name = \'' + fName + ' ' + lName + '\'';
If need further clearance do follow quotes in JavaScript