Executes a SQL statement.
Returns a Promise object or the 'this' object.
The required sql-statement identifies the SQL statement to be executed.
Options is a struct that can have the following items, all of which are optional.
Hostvars is a struct containing name-value pairs that specify input values for the SQL statement.
Wait-state automatically adds a loading icon to the application window while the query is being executed. This is especially useful if the server needs an unusually long time to complete.
Promise determines the return value of this function. If promise has the value 'true' (the default), a Promise object is returned. If promise has the value 'false', the ‘this’ object is returned instead.
Success-function is a function called after the operation has successfully completed.
Error-function is a function called if an error occurs.