PHP Fatal error: Call to a member function query() on a non-object in

Call the function $this-> _db-> Query ($SQL), PHP Fatal error: Call to a member function query() on a non-object in.
At first I thought this function would not work, but later I found out that it was myself $this-> _DB does not exist.
My problem is that static variables are called directly within the class using $DBNAME,
It should be self: : DBNAME
I’ve sorted this out before, but I can’t remember it…

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